## Privoxy &p-version; User Manual

Copyright &my-copy; 2001 - 2004 by Privoxy Developers
$Id: user-manual.sgml,v 1.123.2.39 2004/01/30 22:31:40 oes Exp $

This is here to keep vim syntax file from breaking :/ If I knew enough to fix it, I would. PLEASE DO NOT REMOVE! HB: hal@foobox.net ]]>

The User Manual gives users information on how to install, configure and use Privoxy.

&p-intro;

You can find the latest version of the User Manual at http://www.privoxy.org/user-manual/. Please see the Contact section on how to contact the developers.

## Introduction

This documentation is included with the current &p-status; version of Privoxy, v.&p-version;soon ;-)]]>.

Since this is a &p-status; version, not all new features are well tested. This documentation may be slightly out of sync as a result (especially with CVS sources). And there may be bugs, though hopefully not many! ]]>

### Features

In addition to Internet Junkbuster's traditional features of ad and banner blocking and cookie management, Privoxy provides new features:

&newfeatures;

## Installation

Privoxy is available both in convenient pre-compiled packages for a wide range of operating systems, and as raw source code. For most users, we recommend using the packages, which can be downloaded from our Privoxy Project Page.

Note: If you have a previous Junkbuster or Privoxy installation on your system, you will need to remove it. On some platforms, this may be done for you as part of their installation procedure. (See below for your platform). In any case be sure to backup your old configuration if it is valuable to you. See the note to upgraders section below.

### Binary Packages

How to install the binary packages depends on your operating system:

#### Red Hat, SuSE and Conectiva RPMs

RPMs can be installed with `rpm -Uvh privoxy-&p-version;-1.rpm`, and will use `/etc/privoxy` for the location of configuration files.

Note that on Red Hat, Privoxy will not be automatically started on system boot. You will need to enable that using `chkconfig`, `ntsysv`, or similar methods. Note that SuSE will automatically start Privoxy in the boot process.

If you have problems with failed dependencies, try rebuilding the SRC RPM: `rpm --rebuild privoxy-&p-version;-1.src.rpm`. This will use your locally installed libraries and RPM version.

Also note that if you have a Junkbuster RPM installed on your system, you need to remove it first, because the packages conflict. Otherwise, RPM will try to remove Junkbuster automatically, before installing Privoxy.

#### Debian

DEBs can be installed with `apt-get install privoxy`, and will use `/etc/privoxy` for the location of configuration files.

#### Windows

Just double-click the installer, which will guide you through the installation process. You will find the configuration files in the same directory as you installed Privoxy in. We do not use the registry of Windows.

#### Solaris, NetBSD, FreeBSD, HP-UX

Create a new directory, `cd` to it, then unzip and untar the archive. For the most part, you'll have to figure out where things go.

#### OS/2

First, make sure that no previous installations of Junkbuster and / or Privoxy are left on your system. Check that no Junkbuster or Privoxy objects are in your startup folder.

Then, just double-click the WarpIN self-installing archive, which will guide you through the installation process. A shadow of the Privoxy executable will be placed in your startup folder so it will start automatically whenever OS/2 starts.

The directory you choose to install Privoxy into will contain all of the configuration files.

#### Mac OSX

Unzip the downloaded file (you can either double-click on the file from the finder, or from the desktop if you downloaded it there). Then, double-click on the package installer icon named `Privoxy.pkg` and follow the installation process. Privoxy will be installed in the folder `/Library/Privoxy`. It will start automatically whenever you start up. To prevent it from starting automatically, remove or rename the folder `/Library/StartupItems/Privoxy`.

To start Privoxy by hand, double-click on `StartPrivoxy.command` in the `/Library/Privoxy` folder. Or, type this command in the Terminal:

      /Library/Privoxy/StartPrivoxy.command

You will be prompted for the administrator password.

#### AmigaOS

Copy and then unpack the `lha` archive to a suitable location. All necessary files will be installed into Privoxy directory, including all configuration and log files. To uninstall, just remove this directory.

#### Gentoo

Gentoo source packages (Ebuilds) for Privoxy are contained in the Gentoo Portage Tree (they are not on the download page, but there is a Gentoo section, where you can see when a new Privoxy Version is added to the Portage Tree).

Before installing Privoxy under Gentoo just do first `emerge rsync` to get the latest changes from the Portage tree. With `emerge privoxy` you install the latest version.

Configuration files are in `/etc/privoxy`, the documentation is in `/usr/share/doc/privoxy-&p-version;` and the Log directory is in `/var/log/privoxy`.

### Building from Source

The most convenient way to obtain the Privoxy sources is to download the source tarball from our project page.

If you like to live on the bleeding edge and are not afraid of using possibly unstable development versions, you can check out the up-to-the-minute version directly from the CVS repository or simply download the nightly CVS tarball.

&buildsource;

### Keeping your Installation Up-to-Date

As user feedback comes in and development continues, we will make updated versions of both the main actions file (as a separate package) and the software itself (including the actions file) available for download.

If you wish to receive an email notification whenever we release updates of Privoxy or the actions file, subscribe to our announce mailing list, ijbswa-announce@lists.sourceforge.net.

In order not to loose your personal changes and adjustments when updating to the latest `default.action` file we strongly recommend that you use `user.action` for your customization of Privoxy. See the Chapter on actions files for details.

## Note to Upgraders

There are very significant changes from earlier Junkbuster versions to the current Privoxy. The number, names, syntax, and purposes of configuration files have substantially changed. Junkbuster 2.0.x configuration files will not migrate, Junkbuster 2.9.x and Privoxy configurations will need to be ported. The functionalities of the old `blockfile`, `cookiefile` and `imagelist` are now combined into the actions files. `default.action`, is the main actions file. Local exceptions should best be put into `user.action`.

A filter file (typically `default.filter`) is new as of Privoxy 2.9.x, and provides some of the new sophistication (explained below). `config` is much the same as before.

If upgrading from a 2.0.x version, you will have to use the new config files, and possibly adapt any personal rules from your older files. When porting personal rules over from the old `blockfile` to the new actions files, please note that even the pattern syntax has changed. If upgrading from 2.9.x development versions, it is still recommended to use the new configuration files.

A quick list of things to be aware of before upgrading:

- The default listening port is now 8118 due to a conflict with another service (NAS).

- Some installers may remove earlier versions completely. Save any important configuration files!

- Privoxy is controllable with a web browser at the special URL: http://config.privoxy.org/ (Shortcut: http://p.p/). Many aspects of configuration can be done here, including temporarily disabling Privoxy.

- The primary configuration files for cookie management, ad and banner blocking, and many other aspects of Privoxy configuration are the actions files. It is strongly recommended to become familiar with the new actions concept below, before modifying these files. Locally defined rules should go into `user.action`.

- Some installers may not automatically start Privoxy after installation.

## Quickstart to Using Privoxy

- If upgrading, from versions before 2.9.16, please back up any configuration files. See the Note to Upgraders Section.

- Install Privoxy. See the Installation Section below for platform specific information.

- Advanced users and those who want to offer Privoxy service to more than just their local machine should check the main config file, especially the security-relevant options. These are off by default.

- Start Privoxy, if the installation program has not done this already (may vary according to platform). See the section Starting Privoxy.

- Set your browser to use Privoxy as HTTP and HTTPS (SSL) proxy by setting the proxy configuration for address of `127.0.0.1` and port `8118`. (Junkbuster and earlier versions of Privoxy used port 8000.) See the section Starting Privoxy below for more details on this.

- Flush your browser's disk and memory caches, to remove any cached ad images. If using Privoxy to manage cookies, you should remove any currently stored cookies too.

- A default installation should provide a reasonable starting point for most. There will undoubtedly be occasions where you will want to adjust the configuration, but that can be dealt with as the need arises. Little to no initial configuration is required in most cases.

  See the Configuration section for more configuration options, and how to customize your installation. next section for a quick introduction to how Privoxy blocks ads and banners.]]>

- If you experience ads that slipped through, innocent images that are blocked, or otherwise feel the need to fine-tune Privoxy's behaviour, take a look at the actions files. As a quick start, you might find the richly commented examples helpful. You can also view and edit the actions files through the web-based user interface. The Appendix Anatomy of an Action has hints how to debug actions that misbehave.

- For easy access to Privoxy's most important controls, drag the provided Bookmarklets into your browser's personal toolbar.

- Please see the section Contacting the Developers on how to report bugs or problems with websites or to get help.

- Now enjoy surfing with enhanced comfort and privacy!

### Quickstart to Ad Blocking

Ad blocking is but one of Privoxy's array of features. Many of these features are for the technically minded advanced user. But, ad and banner blocking is surely common ground for everybody.

This section will provide a quick summary of ad blocking so you can get up to speed quickly without having to read the more extensive information provided below, though this is highly recommended.

First a bit of a warning ... blocking ads is much like blocking SPAM: the more aggressive you are about it, the more likely you are to block things that were not intended. So there is a trade off here. If you want extreme ad free browsing, be prepared to deal with more problem sites, and to spend more time adjusting the configuration to solve these unintended consequences. In short, there is not an easy way to eliminate all ads. Either take the easy way and settle for most ads blocked with the default configuration, or jump in and tweak it for your personal surfing habits and preferences.

Secondly, a brief explanation of Privoxy's actions. Actions in this context, are the directives we use to tell Privoxy to perform some task relating to HTTP transactions (i.e. web browsing). We tell Privoxy to take some action. Each action has a unique name and function. While there are many potential actions in Privoxy's arsenal, only a few are used for ad blocking. Actions, and action configuration files, are explained in depth below.

Actions are specified in Privoxy's configuration, followed by one or more URLs to which the action should apply. URLs can actually be URL type patterns that use wildcards so they can apply potentially to a range of similar URLs. The actions, together with the URL patterns are called a section.

When you connect to a website, the full URL will either match one or more of the sections as defined in Privoxy's configuration, or not. If so, then Privoxy will perform the respective actions. If not, then nothing special happens. Furthermore, web pages may contain embedded, secondary URLs that your web browser will use to load additional components of the page, as it parses the original page's HTML content. An ad image for instance, is just an URL embedded in the page somewhere. The image itself may be on the same server, or a server somewhere else on the Internet. Complex web pages will have many such embedded URLs.

The actions we need to know about for ad blocking are: `block`, `handle-as-image`, and `set-image-blocker`:

- `block` - this action stops any contact between your browser and any URL patterns that match this action's configuration. It can be used for blocking ads, but also anything that is determined to be unwanted. By itself, it simply stops any communication with the remote server and sends Privoxy's own built-in BLOCKED page instead to let you now what has happened.

- `handle-as-image` - tells Privoxy to treat this URL as an image. Privoxy's default configuration already does this for all common image types (e.g. GIF), but there are many situations where this is not so easy to determine. So we'll force it in these cases. This is particularly important for ad blocking, since only if we know that it's an image of some kind, can we replace it with an image of our choosing, instead of the Privoxy BLOCKED page (which would only result in a broken image icon). There are some limitations to this though. For instance, you can't just brute-force an image substitution for an entire HTML page in most situations.

- `set-image-blocker` - tells Privoxy what to display in place of an ad image that has hit a block rule. For this to come into play, the URL must match a `block` action somewhere in the configuration, and, it must also match an `handle-as-image` action.

  The configuration options on what to display instead of the ad are:

  - pattern - a checkerboard pattern, so that an ad replacement is obvious. This is the default.
  - blank - A very small empty GIF image is displayed. This is the so-called invisible configuration option.
  - http://<URL> - A redirect to any image anywhere of the user's choosing (advanced usage).

The quickest way to adjust any of these settings is with your browser through the special Privoxy editor at http://config.privoxy.org/show-status (shortcut: http://p.p/show-status). This is an internal page, and does not require Internet access. Select the appropriate actions file, and click Edit. It is best to put personal or local preferences in `user.action` since this is not meant to be overwritten during upgrades, and will over-ride the settings in other files. Here you can insert new actions, and URLs for ad blocking or other purposes, and make other adjustments to the configuration. Privoxy will detect these changes automatically.

A quick and simple step by step example:

- Right click on the ad image to be blocked, then select Copy Link Location from the pop-up menu.

- Set your browser to http://config.privoxy.org/show-status

- Find `user.action` in the top section, and click on Edit:

  #### Actions Files in Use

  [ Screenshot of Actions Files in Use ]

- You should have a section with only `block` listed under Actions:. If not, click a Insert new section below button, and in the new section that just appeared, click the Edit button right under the word Actions:. This will bring up a list of all actions. Find `block` near the top, and click in the Enabled column, then Submit just below the list.

- Now, in the `block` actions section, click the Add button, and paste the URL the browser got from Copy Link Location. Remove the `http://` at the beginning of the URL. Then, click Submit (or OK if in a pop-up window).

- Now go back to the original page, and press SHIFT-Reload (or flush all browser caches). The image should be gone now.

This is a very crude and simple example. There might be good reasons to use a wildcard pattern match to include potentially similar images from the same site. For a more extensive explanation of patterns, and the entire actions concept, see the Actions section.

For advanced users who want to hand edit their config files, you might want to now go to the Actions Files Tutorial. The ideas explained therein also apply to the web-based editor.

## Starting Privoxy

Before launching Privoxy for the first time, you will want to configure your browser(s) to use Privoxy as a HTTP and HTTPS proxy. The default is 127.0.0.1 (or localhost) for the proxy address, and port 8118 (earlier versions used port 8000). This is the one configuration step that must be done!

Please note that Privoxy can only proxy HTTP and HTTPS traffic. It will not work with FTP or other protocols.

### Proxy Configuration (Mozilla)

[ Screenshot of Mozilla Proxy Configuration ]

With Netscape (and Mozilla), this can be set under:

     Edit
       |_
             Preferences
                    |_
                            Advanced
                                  |_
                                        Proxies
                                             |_
                                                    HTTP Proxy

For Internet Explorer:

     Tools
         |_
             Internet Properties
                                |_
                                          Connections
                                                   |_
                                                                LAN Settings

Then, check Use Proxy and fill in the appropriate info (Address: 127.0.0.1, Port: 8118). Include HTTPS (SSL), if you want HTTPS proxy support too.

After doing this, flush your browser's disk and memory caches to force a re-reading of all pages and to get rid of any ads that may be cached. You are now ready to start enjoying the benefits of using Privoxy!

Privoxy is typically started by specifying the main configuration file to be used on the command line. If no configuration file is specified on the command line, Privoxy will look for a file named `config` in the current directory. Except on Win32 where it will try `config.txt`.

### Red Hat and Conectiva

We use a script. Note that Red Hat does not start Privoxy upon booting per default. It will use the file `/etc/privoxy/config` as its main configuration file.

     # /etc/rc.d/init.d/privoxy start

### Debian

We use a script. Note that Debian starts Privoxy upon booting per default. It will use the file `/etc/privoxy/config` as its main configuration file.

     # /etc/init.d/privoxy start

### SuSE

We use a script. It will use the file `/etc/privoxy/config` as its main configuration file. Note that SuSE starts Privoxy upon booting your PC.

     # rcprivoxy start

### Windows

Click on the Privoxy Icon to start Privoxy. If no configuration file is specified on the command line, Privoxy will look for a file named `config.txt`. Note that Windows will automatically start Privoxy upon booting you PC.

### Solaris, NetBSD, FreeBSD, HP-UX and others

Example Unix startup command:

     # /usr/sbin/privoxy /etc/privoxy/config

### OS/2

During installation, Privoxy is configured to start automatically when the system restarts. You can start it manually by double-clicking on the Privoxy icon in the Privoxy folder.

### Mac OSX

During installation, Privoxy is configured to start automatically when the system restarts. To start Privoxy by hand, double-click on the `StartPrivoxy.command` icon in the `/Library/Privoxy` folder. Or, type this command in the Terminal:

      /Library/Privoxy/StartPrivoxy.command

You will be prompted for the administrator password.

### AmigaOS

Start Privoxy (with RUN <>NIL:) in your `startnet` script (AmiTCP), in `s:user-startup` (RoadShow), as startup program in your startup script (Genesis), or as startup action (Miami and MiamiDx). Privoxy will automatically quit when you quit your TCP/IP stack (just ignore the harmless warning your TCP/IP stack may display that Privoxy is still running).

### Gentoo

A script is again used. It will use the file `/etc/privoxy/config` as its main configuration file.

     /etc/init.d/privoxy start

Note that Privoxy is not automatically started at boot time by default. You can change this with the `rc-update` command.

     rc-update add privoxy default

### Command Line Options

Privoxy may be invoked with the following command-line options:

- --version

  Print version info and exit. Unix only.

- --help

  Print short usage info and exit. Unix only.

- --no-daemon

  Don't become a daemon, i.e. don't fork and become process group leader, and don't detach from controlling tty. Unix only.

- --pidfile FILE

  On startup, write the process ID to FILE. Delete the FILE on exit. Failure to create or delete the FILE is non-fatal. If no FILE option is given, no PID file will be used. Unix only.

- --user USER[.GROUP]

  After (optionally) writing the PID file, assume the user ID of USER, and if included the GID of GROUP. Exit if the privileges are not sufficient to do so. Unix only.

- --chroot

  Before changing to the user ID given in the --user option, chroot to that user's home directory, i.e. make the kernel pretend to the Privoxy process that the directory tree starts there. If set up carefully, this can limit the impact of possible vulnerabilities in Privoxy to the files contained in that hierarchy. Unix only.

- configfile

  If no configfile is included on the command line, Privoxy will look for a file named config in the current directory (except on Win32 where it will look for config.txt instead). Specify full path to avoid confusion. If no config file is found, Privoxy will fail to start.

## Privoxy Configuration

All Privoxy configuration is stored in text files. These files can be edited with a text editor. Many important aspects of Privoxy can also be controlled easily with a web browser.

### Controlling Privoxy with Your Web Browser

Privoxy's user interface can be reached through the special URL http://config.privoxy.org/ (shortcut: http://p.p/), which is a built-in page and works without Internet access. You will see the following section:

         Privoxy Menu

              &squf;  View & change the current configuration

              &squf;  View the source code version numbers

              &squf;  View the request headers.

              &squf;  Look up which actions apply to a URL and why

              &squf;  Toggle Privoxy on or off

              &squf;  Documentation

This should be self-explanatory. Note the first item leads to an editor for the actions files, which is where the ad, banner, cookie, and URL blocking magic is configured as well as other advanced features of Privoxy. This is an easy way to adjust various aspects of Privoxy configuration. The actions file, and other configuration files, are explained in detail below.

Toggle Privoxy On or Off is handy for sites that might have problems with your current actions and filters. You can in fact use it as a test to see whether it is Privoxy causing the problem or not. Privoxy continues to run as a proxy in this case, but all manipulation is disabled, i.e. Privoxy acts like a normal forwarding proxy. There is even a toggle Bookmarklet offered, so that you can toggle Privoxy with one click from your browser.

### Configuration Files Overview

For Unix, *BSD and Linux, all configuration files are located in `/etc/privoxy/` by default. For MS Windows, OS/2, and AmigaOS these are all in the same directory as the Privoxy executable.

The installed defaults provide a reasonable starting point, though some settings may be aggressive by some standards. For the time being, the principle configuration files are:

- The main configuration file is named `config` on Linux, Unix, BSD, OS/2, and AmigaOS and `config.txt` on Windows. This is a required file.

- `default.action` (the main actions file) is used to define which actions relating to banner-blocking, images, pop-ups, content modification, cookie handling etc should be applied by default. It also defines many exceptions (both positive and negative) from this default set of actions that enable Privoxy to selectively eliminate the junk, and only the junk, on as many websites as possible.

  Multiple actions files may be defined in `config`. These are processed in the order they are defined. Local customizations and locally preferred exceptions to the default policies as defined in `default.action` (which you will most probably want to define sooner or later) are probably best applied in `user.action`, where you can preserve them across upgrades. `standard.action` is for Privoxy's internal use.

  There is also a web based editor that can be accessed from http://config.privoxy.org/show-status (Shortcut: http://p.p/show-status) for the various actions files.

- `default.filter` (the filter file) can be used to re-write the raw page content, including viewable text as well as embedded HTML and JavaScript, and whatever else lurks on any given web page. The filtering jobs are only pre-defined here; whether to apply them or not is up to the actions files. Only one filter file may be defined.

All files use the `#` character to denote a comment (the rest of the line will be ignored) and understand line continuation through placing a backslash ("`\`") as the very last character in a line. If the `#` is preceded by a backslash, it looses its special function. Placing a `#` in front of an otherwise valid configuration line to prevent it from being interpreted is called "commenting out" that line.

The actions files and `default.filter` can use Perl style regular expressions for maximum flexibility.

After making any changes, there is no need to restart Privoxy in order for the changes to take effect. Privoxy detects such changes automatically. Note, however, that it may take one or two additional requests for the change to take effect. When changing the listening address of Privoxy, these wake up requests must obviously be sent to the old listening address.

While under development, the configuration content is subject to change. The below documentation may not be accurate by the time you read this. Also, what constitutes a default setting, may change, so please check all your configuration files on important issues. ]]>

&config;

## Actions Files

The actions files are used to define what actions Privoxy takes for which URLs, and thus determine how ad images, cookies and various other aspects of HTTP content and transactions are handled, and on which sites (or even parts thereof). There are three such files included with Privoxy with differing purposes:

- `default.action` - is the primary action file that sets the initial values for all actions. It is intended to provide a base level of functionality for Privoxy's array of features. So it is a set of broad rules that should work reasonably well for users everywhere. This is the file that the developers are keeping updated, and making available to users.

- `user.action` - is intended to be for local site preferences and exceptions. As an example, if your ISP or your bank has specific requirements, and need special handling, this kind of thing should go here. This file will not be upgraded.

- `standard.action` - is used by the web based editor, to set various pre-defined sets of rules for the default actions section in `default.action`. These have increasing levels of aggressiveness and have no influence on your browsing unless you select them explicitly in the editor. It is not recommend to edit this file.

  The default profiles, and their associated actions, as pre-defined in `standard.action` are:

  ### Default Configurations

  Feature | Cautious | Medium | Adventuresome
  --- | --- | --- | ---
  Ad-blocking by URL | yes | yes | yes
  Ad-filtering by size | yes | yes | yes
  GIF de-animation | no | yes | yes
  Referer forging | no | yes | yes
  Cookie handling | none | session-only | kill
  Pop-up killing | unsolicited | unsolicited | all
  Fast redirects | no | no | yes
  HTML taming | yes | yes | yes
  JavaScript taming | yes | yes | yes
  Web-bug killing | yes | yes | yes
  Fun text replacements | no | no | yes
  Image tag reordering | no | no | yes
  Ad-filtering by link | no | no | yes
  Demoronizer | no | no | yes

The list of actions files to be used are defined in the main configuration file, and are processed in the order they are defined (e.g. `default.action` is typically process before `user.action`). The content of these can all be viewed and edited from http://config.privoxy.org/show-status.

An actions file typically has multiple sections. If you want to use aliases in an actions file, you have to place the (optional) alias section at the top of that file. Then comes the default set of rules which will apply universally to all sites and pages (be very careful with using such a universal set in `user.action` or any other actions file after `default.action`, because it will override the result from consulting any previous file). And then below that, exceptions to the defined universal policies. You can regard `user.action` as an appendix to `default.action`, with the advantage that is a separate file, which makes preserving your personal settings across Privoxy upgrades easier.

Actions can be used to block anything you want, including ads, banners, or just some obnoxious URL that you would rather not see. Cookies can be accepted or rejected, or accepted only during the current browser session (i.e. not written to disk), content can be modified, JavaScripts tamed, user-tracking fooled, and much more. See below for a complete list of actions.

### Finding the Right Mix

Note that some actions, like cookie suppression or script disabling, may render some sites unusable that rely on these techniques to work properly. Finding the right mix of actions is not always easy and certainly a matter of personal taste. In general, it can be said that the more aggressive your default settings (in the top section of the actions file) are, the more exceptions for trusted sites you will have to make later. If, for example, you want to crunch all cookies per default, you'll have to make exceptions from that rule for sites that you regularly use and that require cookies for actually useful puposes, like maybe your bank, favorite shop, or newspaper.

We have tried to provide you with reasonable rules to start from in the distribution actions files. But there is no general rule of thumb on these things. There just are too many variables, and sites are constantly changing. Sooner or later you will want to change the rules (and read this chapter again :).

### How to Edit

The easiest way to edit the actions files is with a browser by using our browser-based editor, which can be reached from http://config.privoxy.org/show-status. The editor allows both fine-grained control over every single feature on a per-URL basis, and easy choosing from wholesale sets of defaults like Cautious, Medium or Adventuresome. Warning: the Adventuresome setting is not only more aggressive, but includes settings that are fun and subversive, and which some may find of dubious merit!

If you prefer plain text editing to GUIs, you can of course also directly edit the the actions files. Look at `default.action` which is richly commented.

### How Actions are Applied to URLs

Actions files are divided into sections. There are special sections, like the alias sections which will be discussed later. For now let's concentrate on regular sections: They have a heading line (often split up to multiple lines for readability) which consist of a list of actions, separated by whitespace and enclosed in curly braces. Below that, there is a list of URL patterns, each on a separate line.

To determine which actions apply to a request, the URL of the request is compared to all patterns in each action file file. Every time it matches, the list of applicable actions for the URL is incrementally updated, using the heading of the section in which the pattern is located. If multiple matches for the same URL set the same action differently, the last match wins. If not, the effects are aggregated. E.g. a URL might match a regular section with a heading line of `{ +handle-as-image }`, then later another one with just `{ +block }`, resulting in both actions to apply.

You can trace this process for any given URL by visiting http://config.privoxy.org/show-url-info.

More detail on this is provided in the Appendix, Anatomy of an Action.

### Patterns

As mentioned, Privoxy uses patterns to determine what actions might apply to which sites and pages your browser attempts to access. These patterns use wild card type pattern matching to achieve a high degree of flexibility. This allows one expression to be expanded and potentially match against many similar patterns.

Generally, a Privoxy pattern has the form `<domain>/<path>`, where both the `<domain>` and `<path>` are optional. (This is why the special `/` pattern matches all URLs). Note that the protocol portion of the URL pattern (e.g. `http://`) should not be included in the pattern. This is assumed already!

`www.example.com/`

  is a domain-only pattern and will match any request to `www.example.com`, regardless of which document on that server is requested.

`www.example.com`

  means exactly the same. For domain-only patterns, the trailing `/` may be omitted.

`www.example.com/index.html`

  matches only the single document `/index.html` on `www.example.com`.

`/index.html`

  matches the document `/index.html`, regardless of the domain, i.e. on any web server.

`index.html`

  matches nothing, since it would be interpreted as a domain name and there is no top-level domain called `.html`.

#### The Domain Pattern

The matching of the domain part offers some flexible options: if the domain starts or ends with a dot, it becomes unanchored at that end. For example:

`.example.com`

  matches any domain that ENDS in `.example.com`

`www.`

  matches any domain that STARTS with `www.`

`.example.`

  matches any domain that CONTAINS `.example.` (Correctly speaking: It matches any FQDN that contains `example` as a domain.)

Additionally, there are wild-cards that you can use in the domain names themselves. They work pretty similar to shell wild-cards: * stands for zero or more arbitrary characters, ? stands for any single character, you can define character classes in square brackets and all of that can be freely mixed:

`ad*.example.com`

  matches adserver.example.com, ads.example.com, etc but not sfads.example.com

`*ad*.example.com`

  matches all of the above, and then some.

`.?pix.com`

  matches `www.ipix.com`, `pictures.epix.com`, `a.b.c.d.e.upix.com` etc.

`www[1-9a-ez].example.c*`

  matches `www1.example.com`, `www4.example.cc`, `wwwd.example.cy`, `wwwz.example.com` etc., but not `wwww.example.com`.

#### The Path Pattern

Privoxy uses Perl compatible regular expressions (through the PCRE library) for matching the path.

There is an Appendix with a brief quick-start into regular expressions, and full (very technical) documentation on PCRE regex syntax is available on-line at http://www.pcre.org/man.txt. You might also find the Perl man page on regular expressions (`man perlre`) useful, which is available on-line at http://www.perldoc.com/perl5.6/pod/perlre.html.

Note that the path pattern is automatically left-anchored at the /, i.e. it matches as if it would start with a ^ (regular expression speak for the beginning of a line).

Please also note that matching in the path is CASE INSENSITIVE by default, but you can switch to case sensitive at any point in the pattern by using the (?-i) switch: `www.example.com/(?-i)PaTtErN.*` will match only documents whose path starts with `PaTtErN` in exactly this capitalization.

### Actions

All actions are disabled by default, until they are explicitly enabled somewhere in an actions file. Actions are turned on if preceded with a +, and turned off if preceded with a -. So a `+action` means do that action, e.g. `+block` means please block URLs that match the following patterns, and `-block` means don't block URLs that match the following patterns, even if `+block` previously applied.

Again, actions are invoked by placing them on a line, enclosed in curly braces and separated by whitespace, like in `{+some-action -some-other-action{some-parameter}}`, followed by a list of URL patterns, one per line, to which they apply. Together, the actions line and the following pattern lines make up a section of the actions file.

There are three classes of actions:

- Boolean, i.e the action can only be enabled or disabled. Syntax:

        +name        # enable action name
        -name        # disable action name

  Example: `+block`

- Parameterized, where some value is required in order to enable this type of action. Syntax:

        +name{param}  # enable action and set parameter to param,
                     # overwriting parameter from previous match if necessary
        -name         # disable action. The parameter can be omitted

  Note that if the URL matches multiple positive forms of a parameterized action, the last match wins, i.e. the params from earlier matches are simply ignored.

  Example: `+hide-user-agent{ Mozilla 1.0 }`

- Multi-value. These look exactly like parameterized actions, but they behave differently: If the action applies multiple times to the same URL, but with different parameters, all the parameters from all matches are remembered. This is used for actions that can be executed for the same request repeatedly, like adding multiple headers, or filtering through multiple filters. Syntax:

        +name{param}   # enable action and add param to the list of parameters
        -name{param}   # remove the parameter param from the list of parameters
                      # If it was the last one left, disable the action.
        -name          # disable this action completely and remove all parameters from the list

  Examples: `+add-header{X-Fun-Header: Some text}` and `+filter{html-annoyances}`

If nothing is specified in any actions file, no actions are taken. So in this case Privoxy would just be a normal, non-blocking, non-anonymizing proxy. You must specifically enable the privacy and blocking features you need (although the provided default actions files will give a good starting point).

Later defined actions always over-ride earlier ones. So exceptions to any rules you make, should come in the latter part of the file (or in a file that is processed later when using multiple actions files). For multi-valued actions, the actions are applied in the order they are specified. Actions files are processed in the order they are defined in `config` (the default installation has three actions files). It also quite possible for any given URL pattern to match more than one pattern and thus more than one set of actions!

The list of valid Privoxy actions are:

#### add-header

Typical use:

  Confuse log analysis, custom applications

Effect:

  Sends a user defined HTTP header to the web server.

Type:

  Multi-value.

Parameter:

  Any string value is possible. Validity of the defined HTTP headers is not checked. It is recommended that you use the `X-` prefix for custom headers.

Notes:

  This action may be specified multiple times, in order to define multiple headers. This is rarely needed for the typical user. If you don't know what HTTP headers are, you definitely don't need to worry about this one.

Example usage:

      +add-header{X-User-Tracking: sucks}

#### block

Typical use:

  Block ads or other obnoxious content

Effect:

  Requests for URLs to which this action applies are blocked, i.e. the requests are not forwarded to the remote server, but answered locally with a substitute page or image, as determined by the `handle-as-image` and `set-image-blocker` actions.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  Privoxy sends a special BLOCKED page for requests to blocked pages. This page contains links to find out why the request was blocked, and a click-through to the blocked content (the latter only if compiled with the force feature enabled). The BLOCKED page adapts to the available screen space -- it displays full-blown if space allows, or miniaturized and text-only if loaded into a small frame or window. If you are using Privoxy right now, you can take a look at the BLOCKED page.

  A very important exception occurs if both `block` and `handle-as-image`, apply to the same request: it will then be replaced by an image. If `set-image-blocker` (see below) also applies, the type of image will be determined by its parameter, if not, the standard checkerboard pattern is sent.

  It is important to understand this process, in order to understand how Privoxy deals with ads and other unwanted content.

  The `filter` action can perform a very similar task, by blocking banner images and other content through rewriting the relevant URLs in the document's HTML source, so they don't get requested in the first place. Note that this is a totally different technique, and it's easy to confuse the two.

Example usage (section):

      {+block}      # Block and replace with "blocked" page
      .nasty-stuff.example.com

      {+block +handle-as-image} # Block and replace with image
      .ad.doubleclick.net
      .ads.r.us

#### crunch-incoming-cookies

Typical use:

  Prevent the web server from setting any cookies on your system

Effect:

  Deletes any Set-Cookie: HTTP headers from server replies.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  This action is only concerned with incoming cookies. For outgoing cookies, use `crunch-outgoing-cookies`. Use both to disable cookies completely.

  It makes no sense at all to use this action in conjunction with the `session-cookies-only` action, since it would prevent the session cookies from being set. See also `filter-content-cookies`.

Example usage:

      +crunch-incoming-cookies

#### crunch-outgoing-cookies

Typical use:

  Prevent the web server from reading any cookies from your system

Effect:

  Deletes any Cookie: HTTP headers from client requests.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  This action is only concerned with outgoing cookies. For incoming cookies, use `crunch-incoming-cookies`. Use both to disable cookies completely.

  It makes no sense at all to use this action in conjunction with the `session-cookies-only` action, since it would prevent the session cookies from being read.

Example usage:

      +crunch-outgoing-cookies

#### deanimate-gifs

Typical use:

  Stop those annoying, distracting animated GIF images.

Effect:

  De-animate GIF animations, i.e. reduce them to their first or last image.

Type:

  Parameterized.

Parameter:

  last or first

Notes:

  This will also shrink the images considerably (in bytes, not pixels!). If the option first is given, the first frame of the animation is used as the replacement. If last is given, the last frame of the animation is used instead, which probably makes more sense for most banner animations, but also has the risk of not showing the entire last frame (if it is only a delta to an earlier frame).

  You can safely use this action with patterns that will also match non-GIF objects, because no attempt will be made at anything that doesn't look like a GIF.

Example usage:

      +deanimate-gifs{last}

#### downgrade-http-version

Typical use:

  Work around (very rare) problems with HTTP/1.1

Effect:

  Downgrades HTTP/1.1 client requests and server replies to HTTP/1.0.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  This is a left-over from the time when Privoxy didn't support important HTTP/1.1 features well. It is left here for the unlikely case that you experience HTTP/1.1 related problems with some server out there. Not all (optional) HTTP/1.1 features are supported yet, so there is a chance you might need this action.

Example usage (section):

      {+downgrade-http-version}
      problem-host.example.com

#### fast-redirects

Typical use:

  Fool some click-tracking scripts and speed up indirect links

Effect:

  Cut off all but the last valid URL from requests.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  Many sites, like yahoo.com, don't just link to other sites. Instead, they will link to some script on their own servers, giving the destination as a parameter, which will then redirect you to the final target. URLs resulting from this scheme typically look like: http://some.place/click-tracker.cgi?target=http://some.where.else.

  Sometimes, there are even multiple consecutive redirects encoded in the URL. These redirections via scripts make your web browsing more traceable, since the server from which you follow such a link can see where you go to. Apart from that, valuable bandwidth and time is wasted, while your browser ask the server for one redirect after the other. Plus, it feeds the advertisers.

  This feature is currently not very smart and is scheduled for improvement. It is likely to break some sites. You should expect to need possibly many exceptions to this action, if it is enabled by default in `default.action`. Some sites just don't work without it.

Example usage:

      {+fast-redirects}

#### filter

Typical use:

  Get rid of HTML and JavaScript annoyances, banner advertisements (by size), do fun text replacements, etc.

Effect:

  All files of text-based type, most notably HTML and JavaScript, to which this action applies, are filtered on-the-fly through the specified regular expression based substitutions. (Note: as of version 3.0.3 plain text documents are exempted from filtering, because web servers often use the `text/plain` MIME type for all files whose type they don't know.)

Type:

  Parameterized.

Parameter:

  The name of a filter, as defined in the filter file (typically `default.filter`, set by the `filterfile` option in the config file). When used in its negative form, and without parameters, filtering is completely disabled.

Notes:

  For your convenience, there are a number of pre-defined filters available in the distribution filter file that you can use. See the examples below for a list.

  Filtering requires buffering the page content, which may appear to slow down page rendering since nothing is displayed until all content has passed the filters. (It does not really take longer, but seems that way since the page is not incrementally displayed.) This effect will be more noticeable on slower connections.

  This is very powerful feature, but rolling your own filters requires a knowledge of regular expressions and HTML.

  The amount of data that can be filtered is limited to the `buffer-limit` option in the main config file. The default is 4096 KB (4 Megs). Once this limit is exceeded, the buffered data, and all pending data, is passed through unfiltered.

  Inadequate MIME types, such as zipped files, are not filtered at all. (Again, only text-based types except plain text). Encrypted SSL data (from HTTPS servers) cannot be filtered either, since this would violate the integrity of the secure transaction. In some situations it might be necessary to protect certain text, like source code, from filtering by defining appropriate `-filter` sections.

  At this time, Privoxy cannot (yet!) uncompress compressed documents. If you want filtering to work on all documents, even those that would normally be sent compressed, use the `prevent-compression` action in conjunction with `filter`.

  Filtering can achieve some of the same effects as the `block` action, i.e. it can be used to block ads and banners. But the mechanism works quite differently. One effective use, is to block ad banners based on their size (see below), since many of these seem to be somewhat standardized.

  Feedback with suggestions for new or improved filters is particularly welcome!

  The below list has only the names and a one-line description of each predefined filter. There are more verbose explanations of what these filters do in the filter file chapter.

Example usage (with filters from the distribution `default.filter` file). See the Predefined Filters section for more explanation on each:

      +filter{js-annoyances}       # Get rid of particularly annoying JavaScript abuse

      +filter{js-events}           # Kill all JS event bindings (Radically destructive! Only for extra nasty sites)

      +filter{html-annoyances}     # Get rid of particularly annoying HTML abuse

      +filter{content-cookies}     # Kill cookies that come in the HTML or JS content

      +filter{refresh-tags}        # Kill automatic refresh tags (for dial-on-demand setups)

      +filter{unsolicited-popups}  # Disable only unsolicited pop-up windows

      +filter{all-popups}          # Kill all popups in JavaScript and HTML

      +filter{img-reorder}         # Reorder attributes in <img> tags to make the banners-by-* filters more effective

      +filter{banners-by-size}     # Kill banners by size

      +filter{banners-by-link}     # Kill banners by their links to known clicktrackers

      +filter{webbugs}             # Squish WebBugs (1x1 invisible GIFs used for user tracking)

      +filter{tiny-textforms}      # Extend those tiny textareas up to 40x80 and kill the hard wrap

      +filter{jumping-windows}     # Prevent windows from resizing and moving themselves

      +filter{frameset-borders}    # Give frames a border and make them resizable

      +filter{demoronizer}         # Fix MS's non-standard use of standard charsets

      +filter{shockwave-flash}     # Kill embedded Shockwave Flash objects

      +filter{quicktime-kioskmode} # Make Quicktime movies saveable

      +filter{fun}                 # Text replacements for subversive browsing fun!

      +filter{crude-parental}      # Crude parental filtering (demo only)

      +filter{ie-exploits}         # Disable some known Internet Explorer bug exploits

#### handle-as-image

Typical use:

  Mark URLs as belonging to images (so they'll be replaced by images if they get blocked)

Effect:

  This action alone doesn't do anything noticeable. It just marks URLs as images. If the `block` action also applies, the presence or absence of this mark decides whether an HTML blocked page, or a replacement image (as determined by the `set-image-blocker` action) will be sent to the client as a substitute for the blocked content.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  The below generic example section is actually part of `default.action`. It marks all URLs with well-known image file name extensions as images and should be left intact.

  Users will probably only want to use the handle-as-image action in conjunction with `block`, to block sources of banners, whose URLs don't reflect the file type, like in the second example section.

  Note that you cannot treat HTML pages as images in most cases. For instance, (in-line) ad frames require an HTML page to be sent, or they won't display properly. Forcing `handle-as-image` in this situation will not replace the ad frame with an image, but lead to error messages.

Example usage (sections):

      # Generic image extensions:
      #
      {+handle-as-image}
      /.*\.(gif|jpg|jpeg|png|bmp|ico)$

      # These don't look like images, but they're banners and should be
      # blocked as images:
      #
      {+block +handle-as-image}
      some.nasty-banner-server.com/junk.cgi?output=trash

      # Banner source! Who cares if they also have non-image content?
      ad.doubleclick.net

#### hide-forwarded-for-headers

Typical use:

  Improve privacy by hiding the true source of the request

Effect:

  Deletes any existing X-Forwarded-for: HTTP header from client requests, and prevents adding a new one.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  It is fairly safe to leave this on.

  This action is scheduled for improvement: It should be able to generate forged X-Forwarded-for: headers using random IP addresses from a specified network, to make successive requests from the same client look like requests from a pool of different users sharing the same proxy.

Example usage:

      +hide-forwarded-for-headers

#### hide-from-header

Typical use:

  Keep your (old and ill) browser from telling web servers your email address

Effect:

  Deletes any existing From: HTTP header, or replaces it with the specified string.

Type:

  Parameterized.

Parameter:

  Keyword: block, or any user defined value.

Notes:

  The keyword block will completely remove the header (not to be confused with the `block` action).

  Alternately, you can specify any value you prefer to be sent to the web server. If you do, it is a matter of fairness not to use any address that is actually used by a real person.

  This action is rarely needed, as modern web browsers don't send From: headers anymore.

Example usage:

      +hide-from-header{block}

  or

      +hide-from-header{spam-me-senseless@sittingduck.example.com}

#### hide-referrer

Typical use:

  Conceal which link you followed to get to a particular site

Effect:

  Deletes the Referer: (sic) HTTP header from the client request, or replaces it with a forged one.

Type:

  Parameterized.

Parameter:

  - block to delete the header completely.

  - forge to pretend to be coming from the homepage of the server we are talking to.

  - Any other string to set a user defined referrer.

Notes:

  forge is the preferred option here, since some servers will not send images back otherwise, in an attempt to prevent their valuable content from being embedded elsewhere (and hence, without being surrounded by their banners).

  `hide-referer` is an alternate spelling of `hide-referrer` and the two can be can be freely substituted with each other. (referrer is the correct English spelling, however the HTTP specification has a bug - it requires it to be spelled as referer.)

Example usage:

      +hide-referrer{forge}

  or

      +hide-referrer{http://www.yahoo.com/}

#### hide-user-agent

Typical use:

  Conceal your type of browser and client operating system

Effect:

  Replaces the value of the User-Agent: HTTP header in client requests with the specified value.

Type:

  Parameterized.

Parameter:

  Any user-defined string.

Notes:

  This breaks many web sites that depend on looking at this header in order to customize their content for different browsers (which, by the way, is NOT a smart way to do that!).

  Using this action in multi-user setups or wherever different types of browsers will access the same Privoxy is not recommended. In single-user, single-browser setups, you might use it to delete your OS version information from the headers, because it is an invitation to exploit known bugs for your OS. It is also occasionally useful to forge this in order to access sites that won't let you in otherwise (though there may be a good reason in some cases). Example of this: some MSN sites will not let Mozilla enter, yet forging to a Netscape 6.1 user-agent works just fine. (Must be just a silly MS goof, I'm sure :-).

  This action is scheduled for improvement.

Example usage:

      +hide-user-agent{Netscape 6.1 (X11; I; Linux 2.4.18 i686)}

#### kill-popups

Typical use:

  Eliminate those annoying pop-up windows (deprecated)

Effect:

  While loading the document, replace JavaScript code that opens pop-up windows with (syntactically neutral) dummy code on the fly.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  This action is basically a built-in, hardwired special-purpose filter action, but there are important differences: For `kill-popups`, the document need not be buffered, so it can be incrementally rendered while downloading. But `kill-popups` doesn't catch as many pop-ups as `filter{all-popups}` does and is not as smart as `filter{unsolicited-popups}` is.

  Think of it as a fast and efficient replacement for a filter that you can use if you don't want any filtering at all. Note that it doesn't make sense to combine it with any `filter` action, since as soon as one `filter` applies, the whole document needs to be buffered anyway, which destroys the advantage of the `kill-popups` action over its filter equivalent.

  Killing all pop-ups unconditionally is problematic. Many shops and banks rely on pop-ups to display forms, shopping carts etc, and the `filter{unsolicited-popups}` does a fairly good job of catching only the unwanted ones.

  If the only kind of pop-ups that you want to kill are exit consoles (those really nasty windows that appear when you close an other one), you might want to use `filter{js-annoyances}` instead.

Example usage:

      +kill-popups

#### limit-connect

Typical use:

  Prevent abuse of Privoxy as a TCP proxy relay

Effect:

  Specifies to which ports HTTP CONNECT requests are allowable.

Type:

  Parameterized.

Parameter:

  A comma-separated list of ports or port ranges (the latter using dashes, with the minimum defaulting to 0 and the maximum to 65K).

Notes:

  By default, i.e. if no `limit-connect` action applies, Privoxy only allows HTTP CONNECT requests to port 443 (the standard, secure HTTPS port). Use `limit-connect` if more fine-grained control is desired for some or all destinations.

  The CONNECT methods exists in HTTP to allow access to secure websites (https:// URLs) through proxies. It works very simply: the proxy connects to the server on the specified port, and then short-circuits its connections to the client and to the remote server. This can be a big security hole, since CONNECT-enabled proxies can be abused as TCP relays very easily.

  If you don't know what any of this means, there probably is no reason to change this one, since the default is already very restrictive.

Example usages:

      +limit-connect{443}                   # This is the default and need not be specified.
      +limit-connect{80,443}                # Ports 80 and 443 are OK.
      +limit-connect{-3, 7, 20-100, 500-}   # Ports less than 3, 7, 20 to 100 and above 500 are OK.
      +limit-connect{-}                     # All ports are OK (gaping security hole!)

#### prevent-compression

Typical use:

  Ensure that servers send the content uncompressed, so it can be passed through `filter`s

Effect:

  Adds a header to the request that asks for uncompressed transfer.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  More and more websites send their content compressed by default, which is generally a good idea and saves bandwidth. But for the `filter`, `deanimate-gifs` and `kill-popups` actions to work, Privoxy needs access to the uncompressed data. Unfortunately, Privoxy can't yet(!) uncompress, filter, and re-compress the content on the fly. So if you want to ensure that all websites, including those that normally compress, can be filtered, you need to use this action.

  This will slow down transfers from those websites, though. If you use any of the above-mentioned actions, you will typically want to use `prevent-compression` in conjunction with them.

  Note that some (rare) ill-configured sites don't handle requests for uncompressed documents correctly (they send an empty document body). If you use `prevent-compression` per default, you'll have to add exceptions for those sites. See the example for how to do that.

Example usage (sections):

      # Set default:
      #
      {+prevent-compression}
      / # Match all sites

      # Make exceptions for ill sites:
      #
      {-prevent-compression}
      www.debianhelp.org
      www.pclinuxonline.com

#### send-vanilla-wafer

Typical use:

  Feed log analysis scripts with useless data.

Effect:

  Sends a cookie with each request stating that you do not accept any copyright on cookies sent to you, and asking the site operator not to track you.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  The vanilla wafer is a (relatively) unique header and could conceivably be used to track you.

  This action is rarely used and not enabled in the default configuration.

Example usage:

      +send-vanilla-wafer

#### send-wafer

Typical use:

  Send custom cookies or feed log analysis scripts with even more useless data.

Effect:

  Sends a custom, user-defined cookie with each request.

Type:

  Multi-value.

Parameter:

  A string of the form name=value.

Notes:

  Being multi-valued, multiple instances of this action can apply to the same request, resulting in multiple cookies being sent.

  This action is rarely used and not enabled in the default configuration.

Example usage (section):

      {+send-wafer{UsingPrivoxy=true}}
      my-internal-testing-server.void

#### session-cookies-only

Typical use:

  Allow only temporary session cookies (for the current browser session only).

Effect:

  Deletes the expires field from Set-Cookie: server headers. Most browsers will not store such cookies permanently and forget them in between sessions.

Type:

  Boolean.

Parameter:

  N/A

Notes:

  This is less strict than `crunch-incoming-cookies` / `crunch-outgoing-cookies` and allows you to browse websites that insist or rely on setting cookies, without compromising your privacy too badly.

  Most browsers will not permanently store cookies that have been processed by `session-cookies-only` and will forget about them between sessions. This makes profiling cookies useless, but won't break sites which require cookies so that you can log in for transactions. This is generally turned on for all sites, and is the recommended setting.

  It makes no sense at all to use `session-cookies-only` together with `crunch-incoming-cookies` or `crunch-outgoing-cookies`. If you do, cookies will be plainly killed.

  Note that it is up to the browser how it handles such cookies without an expires field. If you use an exotic browser, you might want to try it out to be sure.

  This setting also has no effect on cookies that may have been stored previously by the browser before starting Privoxy. These would have to be removed manually.

  Privoxy also uses the content-cookies filter to block some types of cookies. Content cookies are not effected by `session-cookies-only`.

Example usage:

      +session-cookies-only

#### set-image-blocker

Typical use:

  Choose the replacement for blocked images

Effect:

  This action alone doesn't do anything noticeable. If both `block` and `handle-as-image` also apply, i.e. if the request is to be blocked as an image, then the parameter of this action decides what will be sent as a replacement.

Type:

  Parameterized.

Parameter:

  - pattern to send a built-in checkerboard pattern image. The image is visually decent, scales very well, and makes it obvious where banners were busted.

  - blank to send a built-in transparent image. This makes banners disappear completely, but makes it hard to detect where Privoxy has blocked images on a given page and complicates troubleshooting if Privoxy has blocked innocent images, like navigation icons.

  - target-url to send a redirect to target-url. You can redirect to any image anywhere, even in your local filesystem (via file:/// URL).

    A good application of redirects is to use special Privoxy-built-in URLs, which send the built-in images, as target-url. This has the same visual effect as specifying blank or pattern in the first place, but enables your browser to cache the replacement image, instead of requesting it over and over again.

Notes:

  The URLs for the built-in images are http://config.privoxy.org/send-banner?type=type, where type is either blank or pattern.

  There is a third (advanced) type, called auto. It is NOT to be used in `set-image-blocker`, but meant for use from filters. Auto will select the type of image that would have applied to the referring page, had it been an image.

Example usage:

  Built-in pattern:

      +set-image-blocker{pattern}

  Redirect to the BSD devil:

      +set-image-blocker{http://www.freebsd.org/gifs/dae_up3.gif}

  Redirect to the built-in pattern for better caching:

      +set-image-blocker{http://config.privoxy.org/send-banner?type=pattern}

#### Summary

Note that many of these actions have the potential to cause a page to misbehave, possibly even not to display at all. There are many ways a site designer may choose to design his site, and what HTTP header content, and other criteria, he may depend on. There is no way to have hard and fast rules for all sites. See the Appendix for a brief example on troubleshooting actions.

### Aliases

Custom actions, known to Privoxy as aliases, can be defined by combining other actions. These can in turn be invoked just like the built-in actions. Currently, an alias name can contain any character except space, tab, =, { and }, but we strongly recommend that you only use a to z, 0 to 9, +, and -. Alias names are not case sensitive, and are not required to start with a + or - sign, since they are merely textually expanded.

Aliases can be used throughout the actions file, but they must be defined in a special section at the top of the file! And there can only be one such section per actions file. Each actions file may have its own alias section, and the aliases defined in it are only visible within that file.

There are two main reasons to use aliases: One is to save typing for frequently used combinations of actions, the other one is a gain in flexibility: If you decide once how you want to handle shops by defining an alias called shop, you can later change your policy on shops in one place, and your changes will take effect everywhere in the actions file where the shop alias is used. Calling aliases by their purpose also makes your actions files more readable.

Currently, there is one big drawback to using aliases, though: Privoxy's built-in web-based action file editor honors aliases when reading the actions files, but it expands them before writing. So the effects of your aliases are of course preserved, but the aliases themselves are lost when you edit sections that use aliases with it. This is likely to change in future versions of Privoxy.

Now let's define some aliases...

     # Useful custom aliases we can use later.
     #
     # Note the (required!) section header line and that this section
     # must be at the top of the actions file!
     #
     {{alias}}

     # These aliases just save typing later:
     # (Note that some already use other aliases!)
     #
     +crunch-all-cookies = +crunch-incoming-cookies +crunch-outgoing-cookies
     -crunch-all-cookies = -crunch-incoming-cookies -crunch-outgoing-cookies
     block-as-image      = +block +handle-as-image
     mercy-for-cookies   = -crunch-all-cookies -session-cookies-only -filter{content-cookies}

     # These aliases define combinations of actions
     # that are useful for certain types of sites:
     #
     fragile     = -block -filter -crunch-all-cookies -fast-redirects -hide-referrer -kill-popups
     shop        = -crunch-all-cookies -filter{all-popups} -kill-popups

     # Short names for other aliases, for really lazy people ;-)
     #
     c0 = +crunch-all-cookies
     c1 = -crunch-all-cookies

...and put them to use. These sections would appear in the lower part of an actions file and define exceptions to the default actions (as specified further up for the / pattern):

     # These sites are either very complex or very keen on
     # user data and require minimal interference to work:
     #
     {fragile}
     .office.microsoft.com
     .windowsupdate.microsoft.com
     .nytimes.com

     # Shopping sites:
     # Allow cookies (for setting and retrieving your customer data)
     #
     {shop}
     .quietpc.com
     .worldpay.com   # for quietpc.com
     .scan.co.uk

     # These shops require pop-ups:
     #
     {shop -kill-popups -filter{all-popups}}
      .dabs.com
      .overclockers.co.uk

Aliases like shop and fragile are often used for problem sites that require some actions to be disabled in order to function properly.

### Actions Files Tutorial

The above chapters have shown which actions files there are and how they are organized, how actions are specified and applied to URLs, how patterns work, and how to define and use aliases. Now, let's look at an example `default.action` and `user.action` file and see how all these pieces come together:

#### default.action

Every config file should start with a short comment stating its purpose:

    # Sample default.action file <developers@privoxy.org>

Then, since this is the `default.action` file, the first section is a special section for internal use that you needn't change or worry about:

    ##########################################################################
    # Settings -- Don't change! For internal Privoxy use ONLY.
    ##########################################################################

    {{settings}}
    for-privoxy-version=3.0

After that comes the (optional) alias section. We'll use the example section from the above chapter on aliases, that also explains why and how aliases are used:

    ##########################################################################
    # Aliases
    ##########################################################################
    {{alias}}

     # These aliases just save typing later:
     # (Note that some already use other aliases!)
     #
     +crunch-all-cookies = +crunch-incoming-cookies +crunch-outgoing-cookies
     -crunch-all-cookies = -crunch-incoming-cookies -crunch-outgoing-cookies
     block-as-image      = +block +handle-as-image
     mercy-for-cookies   = -crunch-all-cookies -session-cookies-only -filter{content-cookies}

     # These aliases define combinations of actions
     # that are useful for certain types of sites:
     #
     fragile     = -block -filter -crunch-all-cookies -fast-redirects -hide-referrer -kill-popups
     shop        = -crunch-all-cookies -filter{all-popups} -kill-popups

Now come the regular sections, i.e. sets of actions, accompanied by URL patterns to which they apply. Remember all actions are disabled when matching starts, so we have to explicitly enable the ones we want.

The first regular section is probably the most important. It has only one pattern, `/`, but this pattern matches all URLs. Therefore, the set of actions used in this default section will be applied to all requests as a start. It can be partly or wholly overridden by later matches further down this file, or in user.action, but it will still be largely responsible for your overall browsing experience.

Again, at the start of matching, all actions are disabled, so there is no real need to disable any actions here, but we will do that nonetheless, to have a complete listing for your reference. (Remember: a + preceding the action name enables the action, a - disables!). Also note how this long line has been made more readable by splitting it into multiple lines with line continuation.

    ##########################################################################
    # "Defaults" section:
    ##########################################################################
     { \
     -add-header \
     -block \
     -crunch-incoming-cookies \
     -crunch-outgoing-cookies \
     +deanimate-gifs \
     -downgrade-http-version \
     +fast-redirects \
     +filter{js-annoyances} \
     -filter{js-events} \
     +filter{html-annoyances} \
     -filter{content-cookies} \
     +filter{refresh-tags} \
     +filter{unsolicited-popups} \
     -filter{all-popups} \
     +filter{img-reorder} \
     +filter{banners-by-size} \
     -filter{banners-by-link} \
     +filter{webbugs} \
     -filter{tiny-textforms} \
     +filter{jumping-windows} \
     -filter{frameset-borders} \
     -filter{demoronizer} \
     -filter{shockwave-flash} \
     -filter{quicktime-kioskmode} \
     -filter{fun} \
     -filter{crude-parental} \
     +filter{ie-exploits} \
     -handle-as-image \
     +hide-forwarded-for-headers \
     +hide-from-header{block} \
     +hide-referrer{forge} \
     -hide-user-agent \
     -kill-popups \
     -limit-connect \
     +prevent-compression \
     -send-vanilla-wafer \
     -send-wafer \
     +session-cookies-only \
     +set-image-blocker{pattern} \
     }
     / # forward slash will match *all* potential URL patterns.

The default behavior is now set. Note that some actions, like not hiding the user agent, are part of a general policy that applies universally and won't get any exceptions defined later. Other choices, like not blocking (which is understandably the default!) need exceptions, i.e. we need to specify explicitly what we want to block in later sections.

The first of our specialized sections is concerned with fragile sites, i.e. sites that require minimum interference, because they are either very complex or very keen on tracking you (and have mechanisms in place that make them unusable for people who avoid being tracked). We will simply use our pre-defined `fragile` alias instead of stating the list of actions explicitly:

    ##########################################################################
    # Exceptions for sites that'll break under the default action set:
    ##########################################################################

    # "Fragile" Use a minimum set of actions for these sites (see alias above):
    #
    { fragile }
    .office.microsoft.com           # surprise, surprise!
    .windowsupdate.microsoft.com

Shopping sites are not as fragile, but they typically require cookies to log in, and pop-up windows for shopping carts or item details. Again, we'll use a pre-defined alias:

    # Shopping sites:
    #
    { shop }
    .quietpc.com
    .worldpay.com   # for quietpc.com
    .jungle.com
    .scan.co.uk

The `fast-redirects` action, which we enabled per default above, breaks some sites. So disable it for popular sites where we know it misbehaves:

    { -fast-redirects }
    login.yahoo.com
    edit.*.yahoo.com
    .google.com
    .altavista.com/.*(like|url|link):http
    .altavista.com/trans.*urltext=http
    .nytimes.com

It is important that Privoxy knows which URLs belong to images, so that if they are to be blocked, a substitute image can be sent, rather than an HTML page. Contacting the remote site to find out is not an option, since it would destroy the loading time advantage of banner blocking, and it would feed the advertisers (in terms of money and information). We can mark any URL as an image with the `handle-as-image` action, and marking all URLs that end in a known image file extension is a good start:

    ##########################################################################
    # Images:
    ##########################################################################

    # Define which file types will be treated as images, in case they get
    # blocked further down this file:
    #
    { +handle-as-image }
    /.*\.(gif|jpe?g|png|bmp|ico)$

And then there are known banner sources. They often use scripts to generate the banners, so it won't be visible from the URL that the request is for an image. Hence we block them and mark them as images in one go, with the help of our `block-as-image` alias defined above. (We could of course just as well use `+block +handle-as-image` here.) Remember that the type of the replacement image is chosen by the `set-image-blocker` action. Since all URLs have matched the default section with its `+set-image-blocker{pattern}` action before, it still applies and needn't be repeated:

    # Known ad generators:
    #
    { block-as-image }
    ar.atwola.com
    .ad.doubleclick.net
    .ad.*.doubleclick.net
    .a.yimg.com/(?:(?!/i/).)*$
    .a[0-9].yimg.com/(?:(?!/i/).)*$
    bs*.gsanet.com
    bs*.einets.com
    .qkimg.net

One of the most important jobs of Privoxy is to block banners. A huge bunch of them are already blocked by the `filter{banners-by-size}` action, which we enabled above, and which deletes the references to banner images from the pages while they are loaded, so the browser doesn't request them anymore, and hence they don't need to be blocked here. But this naturally doesn't catch all banners, and some people choose not to use filters, so we need a comprehensive list of patterns for banner URLs here, and apply the `block` action to them.

First comes a bunch of generic patterns, which do most of the work, by matching typical domain and path name components of banners. Then comes a list of individual patterns for specific sites, which is omitted here to keep the example short:

    ##########################################################################
    # Block these fine banners:
    ##########################################################################
    { +block }

    # Generic patterns:
    #
    ad*.
    .*ads.
    banner?.
    count*.
    /.*count(er)?\.(pl|cgi|exe|dll|asp|php[34]?)
    /(?:.*/)?(publicite|werbung|rekla(ma|me|am)|annonse|maino(kset|nta|s)?)/

    # Site-specific patterns (abbreviated):
    #
    .hitbox.com

You wouldn't believe how many advertisers actually call their banner servers ads.company.com, or call the directory in which the banners are stored simply banners. So the above generic patterns are surprisingly effective.

But being very generic, they necessarily also catch URLs that we don't want to block. The pattern `.*ads.` e.g. catches nasty-ads.nasty-corp.com as intended, but also downloads.sourcefroge.net or adsl.some-provider.net. So here come some well-known exceptions to the `+block` section above.

Note that these are exceptions to exceptions from the default! Consider the URL downloads.sourcefroge.net: Initially, all actions are deactivated, so it wouldn't get blocked. Then comes the defaults section, which matches the URL, but just deactivates the `block` action once again. Then it matches `.*ads.`, an exception to the general non-blocking policy, and suddenly `+block` applies. And now, it'll match `.*loads.`, where `-block` applies, so (unless it matches again further down) it ends up with no `block` action applying.

    ##########################################################################
    # Save some innocent victims of the above generic block patterns:
    ##########################################################################

    # By domain:
    #
    { -block }
    adv[io]*.  # (for advogato.org and advice.*)
    adsl.      # (has nothing to do with ads)
    ad[ud]*.   # (adult.* and add.*)
    .edu       # (universities don't host banners (yet!))
    .*loads.   # (downloads, uploads etc)

    # By path:
    #
    /.*loads/

    # Site-specific:
    #
    www.globalintersec.com/adv # (adv = advanced)
    www.ugu.com/sui/ugu/adv

Filtering source code can have nasty side effects, so make an exception for our friends at sourceforge.net, and all paths with cvs in them. Note that `-filter` disables all filters in one fell swoop!

    # Don't filter code!
    #
    { -filter }
    /.*cvs
    .sourceforge.net

The actual `default.action` is of course more comprehensive, but we hope this example made clear how it works.

#### user.action

So far we are painting with a broad brush by setting general policies, which would be a reasonable starting point for many people. Now, you might want to be more specific and have customized rules that are more suitable to your personal habits and preferences. These would be for narrowly defined situations like your ISP or your bank, and should be placed in `user.action`, which is parsed after all other actions files and hence has the last word, over-riding any previously defined actions. `user.action` is also a safe place for your personal settings, since `default.action` is actively maintained by the Privoxy developers and you'll probably want to install updated versions from time to time.

So let's look at a few examples of things that one might typically do in `user.action`:

    # My user.action file. <fred@foobar.com>

As aliases are local to the actions file that they are defined in, you can't use the ones from `default.action`, unless you repeat them here:

    # Aliases are local to the file they are defined in.
    # (Re-)define aliases for this file:
    #
    {{alias}}
    #
    # These aliases just save typing later, and the alias names should
    # be self explanatory.
    #
    +crunch-all-cookies = +crunch-incoming-cookies +crunch-outgoing-cookies
    -crunch-all-cookies = -crunch-incoming-cookies -crunch-outgoing-cookies
     allow-all-cookies  = -crunch-all-cookies -session-cookies-only
     allow-popups       = -filter{all-popups} -kill-popups
    +block-as-image     = +block +handle-as-image
    -block-as-image     = -block

    # These aliases define combinations of actions that are useful for
    # certain types of sites:
    #
    fragile     = -block -crunch-all-cookies -filter -fast-redirects -hide-referrer -kill-popups
    shop        = -crunch-all-cookies allow-popups

    # Allow ads for selected useful free sites:
    #
    allow-ads   = -block -filter{banners-by-size} -filter{banners-by-link}

Say you have accounts on some sites that you visit regularly, and you don't want to have to log in manually each time. So you'd like to allow persistent cookies for these sites. The `allow-all-cookies` alias defined above does exactly that, i.e. it disables crunching of cookies in any direction, and the processing of cookies to make them only temporary.

    { allow-all-cookies }
    sourceforge.net
    sunsolve.sun.com
    .slashdot.org
    .yahoo.com
    .msdn.microsoft.com
    .redhat.com

Your bank is allergic to some filter, but you don't know which, so you disable them all:

    { -filter }
    .your-home-banking-site.com

Some file types you may not want to filter for various reasons:

    # Technical documentation is likely to contain strings that might
    # erroneously get altered by the JavaScript-oriented filters:
    #
    .tldp.org
    /(.*/)?selfhtml/

    # And this stupid host sends streaming video with a wrong MIME type,
    # so that Privoxy thinks it is getting HTML and starts filtering:
    #
    stupid-server.example.com/

Example of a simple block action. Say you've seen an ad on your favourite page on example.com that you want to get rid of. You have right-clicked the image, selected copy image location and pasted the URL below while removing the leading http://, into a `{ +block }` section. Note that `{ +handle-as-image }` need not be specified, since all URLs ending in `.gif` will be tagged as images by the general rules as set in default.action anyway:

    { +block }
    www.example.com/nasty-ads/sponsor.gif
    another.popular.site.net/more/junk/here/

The URLs of dynamically generated banners, especially from large banner farms, often don't use the well-known image file name extensions, which makes it impossible for Privoxy to guess the file type just by looking at the URL. You can use the `+block-as-image` alias defined above for these cases. Note that objects which match this rule but then turn out NOT to be an image are typically rendered as a broken image icon by the browser. Use cautiously.

    { +block-as-image }
    .doubleclick.net
    /Realmedia/ads/
    ar.atwola.com/

Now you noticed that the default configuration breaks Forbes Magazine, but you were too lazy to find out which action is the culprit, and you were again too lazy to give feedback, so you just used the `fragile` alias on the site, and -- whoa! -- it worked. The `fragile` aliases disables those actions that are most likely to break a site. Also, good for testing purposes to see if it is Privoxy that is causing the problem or not.

    { fragile }
    .forbes.com

You like the fun text replacements in `default.filter`, but it is disabled in the distributed actions file. (My colleagues on the team just don't have a sense of humour, that's why! ;-). So you'd like to turn it on in your private, update-safe config, once and for all:

    { +filter{fun} }
    / # For ALL sites!

Note that the above is not really a good idea: There are exceptions to the filters in `default.action` for things that really shouldn't be filtered, like code on CVS->Web interfaces. Since `user.action` has the last word, these exceptions won't be valid for the fun filtering specified here.

You might also worry about how your favourite free websites are funded, and find that they rely on displaying banner advertisements to survive. So you might want to specifically allow banners for those sites that you feel provide value to you:

    { allow-ads }
    .sourceforge.net
    .slashdot.org
    .osdn.net

Note that `allow-ads` has been aliased to `-block`, `-filter{banners-by-size}`, and `-filter{banners-by-link}` above.

`user.action` is generally the best place to define exceptions and additions to the default policies of `default.action`. Some actions are safe to have their default policies set here though. So let's set a default policy to have a blank image as opposed to the checkerboard pattern for ALL sites. / of course matches all URL paths and patterns:

    { +set-image-blocker{blank} }
    / # ALL sites

## The Filter File

All text substitutions that can be invoked through the `filter` action must first be defined in the filter file, which is typically called `default.filter` and which can be selected through the `filterfile` config option.

Typical reasons for doing such substitutions are to eliminate common annoyances in HTML and JavaScript, such as pop-up windows, exit consoles, crippled windows without navigation tools, the infamous <BLINK> tag etc, to suppress images with certain width and height attributes (standard banner sizes or web-bugs), or just to have fun. The possibilities are endless.

Filtering works on any text-based document type, including HTML, JavaScript, CSS etc. (all `text/*` MIME types, except `text/plain`). Substitutions are made at the source level, so if you want to roll your own filters, you should be familiar with HTML syntax.

Just like the actions files, the filter file is organized in sections, which are called filters here. Each filter consists of a heading line, that starts with the keyword `FILTER:`, followed by the filter's name, and a short (one line) description of what it does. Below that line come the jobs, i.e. lines that define the actual text substitutions. By convention, the name of a filter should describe what the filter eliminates. The comment is used in the web-based user interface.

Once a filter called name has been defined in the filter file, it can be invoked by using an action of the form +`filter{name}` in any actions file.

A filter header line for a filter called foo could look like this:

    FILTER: foo Replace all "foo" with "bar"

Below that line, and up to the next header line, come the jobs that define what text replacements the filter executes. They are specified in a syntax that imitates Perl's `s///` operator. If you are familiar with Perl, you will find this to be quite intuitive, and may want to look at the PCRS man page for the subtle differences to Perl behaviour. Most notably, the non-standard option letter `U` is supported, which turns the default to ungreedy matching.

If you are new to regular expressions, you might want to take a look at the Appendix on regular expressions, and see the Perl manual for the `s///` operator's syntax and Perl-style regular expressions in general. The below examples might also help to get you started.

### Filter File Tutorial

Now, let's complete our foo filter. We have already defined the heading, but the jobs are still missing. Since all it does is to replace foo with bar, there is only one (trivial) job needed:

    s/foo/bar/

But wait! Didn't the comment say that all occurrences of foo should be replaced? Our current job will only take care of the first foo on each page. For global substitution, we'll need to add the `g` option:

    s/foo/bar/g

Our complete filter now looks like this:

    FILTER: foo Replace all "foo" with "bar"
    s/foo/bar/g

Let's look at some real filters for more interesting examples. Here you see a filter that protects against some common annoyances that arise from JavaScript abuse. Let's look at its jobs one after the other:

    FILTER: js-annoyances Get rid of particularly annoying JavaScript abuse

    # Get rid of JavaScript referrer tracking. Test page: http://www.randomoddness.com/untitled.htm
    #
    s|(<script.*)document\.referrer(.*</script>)|$1"Not Your Business!"$2|Usg

Following the header line and a comment, you see the job. Note that it uses `|` as the delimiter instead of `/`, because the pattern contains a forward slash, which would otherwise have to be escaped by a backslash (`\`).

Now, let's examine the pattern: it starts with the text `<script.*` enclosed in parentheses. Since the dot matches any character, and `*` means: Match an arbitrary number of the element left of myself, this matches <script, followed by any text, i.e. it matches the whole page, from the start of the first <script> tag.

That's more than we want, but the pattern continues: `document\.referrer` matches only the exact string document.referrer. The dot needed to be escaped, i.e. preceded by a backslash, to take away its special meaning as a joker, and make it just a regular dot. So far, the meaning is: Match from the start of the first <script> tag in a the page, up to, and including, the text document.referrer, if both are present in the page (and appear in that order).

But there's still more pattern to go. The next element, again enclosed in parentheses, is `.*</script>`. You already know what `.*` means, so the whole pattern translates to: Match from the start of the first <script> tag in a page to the end of the last <script> tag, provided that the text document.referrer appears somewhere in between.

This is still not the whole story, since we have ignored the options and the parentheses: The portions of the page matched by sub-patterns that are enclosed in parentheses, will be remembered and be available through the variables `$1, $2, ...` in the substitute. The `U` option switches to ungreedy matching, which means that the first `.*` in the pattern will only eat up all text in between <script and the first occurrence of document.referrer, and that the second `.*` will only span the text up to the first </script> tag. Furthermore, the `s` option says that the match may span multiple lines in the page, and the `g` option again means that the substitution is global.

So, to summarize, the pattern means: Match all scripts that contain the text document.referrer. Remember the parts of the script from (and including) the start tag up to (and excluding) the string document.referrer as `$1`, and the part following that string, up to and including the closing tag, as `$2`.

Now the pattern is deciphered, but wasn't this about substituting things? So lets look at the substitute: `$1"Not Your Business!"$2` is easy to read: The text remembered as `$1`, followed by `"Not Your Business!"` (including the quotation marks!), followed by the text remembered as `$2`. This produces an exact copy of the original string, with the middle part (the document.referrer) replaced by `"Not Your Business!"`.

The whole job now reads: Replace document.referrer by `"Not Your Business!"` wherever it appears inside a <script&gt tag. Note that this job won't break JavaScript syntax, since both the original and the replacement are syntactically valid string objects. The script just won't have access to the referrer information anymore.

We'll show you two other jobs from the JavaScript taming department, but this time only point out the constructs of special interest:

    # The status bar is for displaying link targets, not pointless blahblah
    #
    s/window\.status\s*=\s*(['"]).*?\1/dUmMy=1/ig

`\s` stands for whitespace characters (space, tab, newline, carriage return, form feed), so that `\s*` means: zero or more whitespace. The `?` in `.*?` makes this matching of arbitrary text ungreedy. (Note that the `U` option is not set). The `['"]` construct means: a single or a double quote. Finally, `\1` is a backreference to the first parenthesis just like `$1` above, with the difference that in the pattern, a backslash indicates a backreference, whereas in the substitute, it's the dollar.

So what does this job do? It replaces assignments of single- or double-quoted strings to the window.status object with a dummy assignment (using a variable name that is hopefully odd enough not to conflict with real variables in scripts). Thus, it catches many cases where e.g. pointless descriptions are displayed in the status bar instead of the link target when you move your mouse over links.

    # Kill OnUnload popups. Yummy. Test: http://www.zdnet.com/zdsubs/yahoo/tree/yfs.html
    #
    s/(<body [^>]*)onunload(.*>)/$1never$2/iU

Including the OnUnload event binding in the HTML DOM was a CRIME. When I close a browser window, I want it to close and die. Basta. This job replaces the onunload attribute in <body&gt tags with the dummy word `never`. Note that the `i` option makes the pattern matching case-insensitive. Also note that ungreedy matching alone doesn't always guarantee a minimal match: In the first parenthesis, we had to use `[^>]*` instead of `.*` to prevent the match from exceeding the <body&gt tag if it doesn't contain OnUnload, but the page's content does.

The last example is from the fun department:

    FILTER: fun Fun text replacements

    # Spice the daily news:
    #
    s/microsoft(?!\.com)/MicroSuck/ig

Note the `(?!\.com)` part (a so-called negative lookahead) in the job's pattern, which means: Don't match, if the string .com appears directly following microsoft in the page. This prevents links to microsoft.com from being trashed, while still replacing the word everywhere else.

    # Buzzword Bingo (example for extended regex syntax)
    #
    s* industry[ -]leading \
    |  cutting[ -]edge \
    |  customer[ -]focused \
    |  market[ -]driven \
    |  award[ -]winning # Comments are OK, too! \
    |  high[ -]performance \
    |  solutions[ -]based \
    |  unmatched \
    |  unparalleled \
    |  unrivalled \
    *<font color="red"><b>BINGO!</b></font> \
    *igx

The `x` option in this job turns on extended syntax, and allows for e.g. the liberal use of (non-interpreted!) whitespace for nicer formatting.

You get the idea?

### The Pre-defined Filters

The distribution `default.filter` file contains a selection of pre-defined filters for your convenience:

js-annoyances

  The purpose of this filter is to get rid of particularly annoying JavaScript abuse. To that end, it

  - replaces JavaScript references to the browser's referrer information with the string "Not Your Business!". This compliments the `hide-referrer` action on the content level.

  - removes the bindings to the DOM's unload event which we feel has no right to exist and is responsible for most exit consoles, i.e. nasty windows that pop up when you close another one.

  - removes code that causes new windows to be opened with undesired properties, such as being full-screen, non-resizable, without location, status or menu bar etc.

js-events

  This is a very radical measure. It removes virtually all JavaScript event bindings, which means that scripts can not react to user actions such as mouse movements or clicks, window resizing etc, anymore.

  We strongly discourage using this filter as a default since it breaks many legitimate scripts. It is meant for use only on extra-nasty sites (should you really need to go there).

html-annoyances

  This filter will undo many common instances of HTML based abuse.

  The `BLINK` and `MARQUEE` tags are neutralized (yeah baby!), and browser windows will be created as resizable (as of course they should be!), and will have location, scroll and menu bars -- even if specified otherwise.

content-cookies

  Most cookies are set in the HTTP dialogue, where they can be intercepted by the `crunch-incoming-cookies` and `crunch-outgoing-cookies` actions. But web sites increasingly make use of HTML meta tags and JavaScript to sneak cookies to the browser on the content level.

  This filter disables HTML and JavaScript code that reads or sets cookies. Use it wherever you would also use the cookie crunch actions.

refresh tags

  Disable any refresh tags if the interval is greater than nine seconds (so that redirections done via refresh tags are not destroyed). This is useful for dial-on-demand setups, or for those who find this HTML feature annoying.

unsolicited-popups

  This filter attempts to prevent only unsolicited pop-up windows from opening, yet still allow pop-up windows that the user has explicitly chosen to open. It was added in version 3.0.1, as an improvement over earlier such filters.

  Technical note: The filter works by redefining the window.open JavaScript function to a dummy function during the loading and rendering phase of each HTML page access, and restoring the function afterwards.

all-popups

  Attempt to prevent all pop-up windows from opening. Note this should be used with more discretion than the above, since it is more likely to break some sites that require pop-ups for normal usage. Use with caution.

img-reorder

  This is a helper filter that has no value if used alone. It makes the `banners-by-size` and `banners-by-link` (see below) filters more effective and should be enabled together with them.

banners-by-size

  This filter removes image tags purely based on what size they are. Fortunately for us, many ads and banner images tend to conform to certain standardized sizes, which makes this filter quite effective for ad stripping purposes.

  Occasionally this filter will cause false positives on images that are not ads, but just happen to be of one of the standard banner sizes.

banners-by-link

  This is an experimental filter that attempts to kill any banners if their URLs seem to point to known or suspected click trackers. It is currently not of much value and is not recommended for use by default.

webbugs

  Webbugs are small, invisible images (technically 1X1 GIF images), that are used to track users across websites, and collect information on them. As an HTML page is loaded by the browser, an embedded image tag causes the browser to contact a third-party site, disclosing the tracking information through the requested URL and/or cookies for that third-party domain, without the use ever becoming aware of the interaction with the third-party site. HTML-ized spam also uses a similar technique to verify email addresses.

  This filter removes the HTML code that loads such webbugs.

tiny-textforms

  A rather special-purpose filter that can be used to enlarge textareas (those multi-line text boxes in web forms) and turn off hard word wrap in them. It was written for the sourceforge.net tracker system where such boxes are a nuisance, but it can be handy on other sites, too.

  It is not recommended to use this filter as a default.

jumping-windows

  Many consider windows that move, or resize themselves to be abusive. This filter neutralizes the related JavaScript code. Note that some sites might not display or behave as intended when using this filter.

frameset-borders

  Some web designers seem to assume that everyone in the world will view their web sites using the same browser brand and version, screen resolution etc, because only that assumption could explain why they'd use static frame sizes, yet prevent their frames from being resized by the user, should they be too small to show their whole content.

  This filter removes the related HTML code. It should only be applied to sites which need it.

demoronizer

  Many Microsoft products that generate HTML use non-standard extensions (read: violations) of the ISO 8859-1 aka Latin-1 character set. This causes those HTML documents to display with errors on standard-compliant platforms.

  This filter translates the MS-only characters into Latin-1 equivalents. It is not necessary when using MS products, and will cause corruption of all documents that use 8-bit character sets other than Latin-1. It's mostly worthwhile for Europeans on non-MS platforms, if wierd garbage characters sometimes appear on some pages.

shockwave-flash

  A filter for shockwave haters. As the name suggests, this filter strips code out of web pages that is used to embed shockwave flash objects.

quicktime-kioskmode

  Change HTML code that embeds Quicktime objects so that kioskmode, which prevents saving, is disabled.

fun

  Text replacements for subversive browsing fun. Make fun of your favorite Monopolist or play buzzword bingo.

crude-parental

  A demonstration-only filter that shows how Privoxy can be used to delete web content on a keyword basis.

ie-exploits

  A collection of text replacements to disable malicious HTML and JavaScript code that exploits known security holes in Internet Explorer.

  Presently, it only protects against Nimda and a cross-site scripting bug, and would need active maintenance to provide more substantial protection.

site-specifics

  Some web sites have very specific problems, the cure for which doesn't apply anywhere else, or could even cause damage on other sites.

  This is a collection of such site-specific cures which should only be applied to the sites they were intended for, which is what the supplied `default.action` file does. Users shouldn't need to change anything regarding this filter.

## Templates

All Privoxy built-in pages, i.e. error pages such as the 404 - No Such Domain error page, the BLOCKED page and all pages of its web-based user interface, are generated from templates. (Privoxy must be running for the above links to work as intended.)

These templates are stored in a subdirectory of the configuration directory called `templates`. On Unixish platforms, this is typically `/etc/privoxy/templates/`.

The templates are basically normal HTML files, but with place-holders (called symbols or exports), which Privoxy fills at run time. You can edit the templates with a normal text editor, should you want to customize them. (Not recommended for the casual user). Note that just like in configuration files, lines starting with `#` are ignored when the templates are filled in.

The place-holders are of the form `@name@`, and you will find a list of available symbols, which vary from template to template, in the comments at the start of each file. Note that these comments are not always accurate, and that it's probably best to look at the existing HTML code to find out which symbols are supported and what they are filled in with.

A special application of this substitution mechanism is to make whole blocks of HTML code disappear when a specific symbol is set. We use this for many purposes, one of them being to include the beta warning in all our user interface (CGI) pages when Privoxy in in an alpha or beta development stage:

    <!-- @if-unstable-start -->

      ... beta warning HTML code goes here ...

    <!-- if-unstable-end@ -->

If the "unstable" symbol is set, everything in between and including `@if-unstable-start` and `if-unstable-end@` will disappear, leaving nothing but an empty comment:

    <!--  -->

There's also an if-then-else construct and an `#include` mechanism, but you'll sure find out if you are inclined to edit the templates ;-)

All templates refer to a style located at `http://config.privoxy.org/send-stylesheet`. This is, of course, locally served by Privoxy and the source for it can be found and edited in the `cgi-style.css` template.

## Contacting the Developers, Bug Reporting and Feature Requests

&contacting;

## Privoxy Copyright, License and History

&copyright;

### License

&license;

### History

&history;

### Authors

&p-authors;

## See Also

&seealso;

## Appendix

### Regular Expressions

Privoxy uses Perl-style regular expressions in its actions files and filter file, through the PCRE and PCRS libraries.

If you are reading this, you probably don't understand what regular expressions are, or what they can do. So this will be a very brief introduction only. A full explanation would require a book ;-)

Regular expressions provide a language to describe patterns that can be run against strings of characters (letter, numbers, etc), to see if they match the string or not. The patterns are themselves (sometimes complex) strings of literal characters, combined with wild-cards, and other special characters, called meta-characters. The meta-characters have special meanings and are used to build complex patterns to be matched against. Perl Compatible Regular Expressions are an especially convenient dialect of the regular expression language.

To make a simple analogy, we do something similar when we use wild-card characters when listing files with the `dir` command in DOS. `*.*` matches all filenames. The special character here is the asterisk which matches any and all characters. We can be more specific and use `?` to match just individual characters. So dir file?.text would match file1.txt, file2.txt, etc. We are pattern matching, using a similar technique to regular expressions!

Regular expressions do essentially the same thing, but are much, much more powerful. There are many more special characters and ways of building complex patterns however. Let's look at a few of the common ones, and then some examples:

- . - Matches any single character, e.g. a, A, 4, :, or @.

- ? - The preceding character or expression is matched ZERO or ONE times. Either/or.

- + - The preceding character or expression is matched ONE or MORE times.

- * - The preceding character or expression is matched ZERO or MORE times.

- \ - The escape character denotes that the following character should be taken literally. This is used where one of the special characters (e.g. .) needs to be taken literally and not as a special meta-character. Example: example\.com, makes sure the period is recognized only as a period (and not expanded to its meta-character meaning of any single character).

- [] - Characters enclosed in brackets will be matched if any of the enclosed characters are encountered. For instance, [0-9] matches any numeric digit (zero through nine). As an example, we can combine this with + to match any digit one of more times: [0-9]+.

- () - parentheses are used to group a sub-expression, or multiple sub-expressions.

- | - The bar character works like an or conditional statement. A match is successful if the sub-expression on either side of | matches. As an example: /(this|that) example/ uses grouping and the bar character and would match either this example or that example, and nothing else.

These are just some of the ones you are likely to use when matching URLs with Privoxy, and is a long way from a definitive list. This is enough to get us started with a few simple examples which may be more illuminating:

`/.*/banners/.*` - A simple example that uses the common combination of . and * to denote any character, zero or more times. In other words, any string at all. So we start with a literal forward slash, then our regular expression pattern (.*) another literal forward slash, the string banners, another forward slash, and lastly another .*. We are building a directory path here. This will match any file with the path that has a directory named banners in it. The .* matches any characters, and this could conceivably be more forward slashes, so it might expand into a much longer looking path. For example, this could match: /eye/hate/spammers/banners/annoy_me_please.gif, or just /banners/annoying.html, or almost an infinite number of other possible combinations, just so it has banners in the path somewhere.

A now something a little more complex:

`/.*/adv((er)?ts?|ertis(ing|ements?))?/` - We have several literal forward slashes again (/), so we are building another expression that is a file path statement. We have another .*, so we are matching against any conceivable sub-path, just so it matches our expression. The only true literal that must match our pattern is adv, together with the forward slashes. What comes after the adv string is the interesting part.

Remember the ? means the preceding expression (either a literal character or anything grouped with (...) in this case) can exist or not, since this means either zero or one match. So ((er)?ts?|ertis(ing|ements?)) is optional, as are the individual sub-expressions: (er), (ing|ements?), and the s. The | means or. We have two of those. For instance, (ing|ements?), can expand to match either ing OR ements?. What is being done here, is an attempt at matching as many variations of advertisement, and similar, as possible. So this would expand to match just adv, or advert, or adverts, or advertising, or advertisement, or advertisements. You get the idea. But it would not match advertizements (with a z). We could fix that by changing our regular expression to: /.*/adv((er)?ts?|erti(s|z)(ing|ements?))?/, which would then match either spelling.

`/.*/advert[0-9]+\.(gif|jpe?g)` - Again another path statement with forward slashes. Anything in the square brackets [] can be matched. This is using 0-9 as a shorthand expression to mean any digit one through nine. It is the same as saying 0123456789. So any digit matches. The + means one or more of the preceding expression must be included. The preceding expression here is what is in the square brackets -- in this case, any digit one through nine. Then, at the end, we have a grouping: (gif|jpe?g). This includes a |, so this needs to match the expression on either side of that bar character also. A simple gif on one side, and the other side will in turn match either jpeg or jpg, since the ? means the letter e is optional and can be matched once or not at all. So we are building an expression here to match image GIF or JPEG type image file. It must include the literal string advert, then one or more digits, and a . (which is now a literal, and not a special character, since it is escaped with \), and lastly either gif, or jpeg, or jpg. Some possible matches would include: //advert1.jpg, /nasty/ads/advert1234.gif, /banners/from/hell/advert99.jpg. It would not match advert1.gif (no leading slash), or /adverts232.jpg (the expression does not include an s), or /advert1.jsp (jsp is not in the expression anywhere).

We are barely scratching the surface of regular expressions here so that you can understand the default Privoxy configuration files, and maybe use this knowledge to customize your own installation. There is much, much more that can be done with regular expressions. Now that you know enough to get started, you can learn more on your own :/

More reading on Perl Compatible Regular expressions: http://www.perldoc.com/perl5.6/pod/perlre.html

For information on regular expression based substitutions and their applications in filters, please see the filter file tutorial in this manual.

### Privoxy's Internal Pages

Since Privoxy proxies each requested web page, it is easy for Privoxy to trap certain special URLs. In this way, we can talk directly to Privoxy, and see how it is configured, see how our rules are being applied, change these rules and other configuration options, and even turn Privoxy's filtering off, all with a web browser.

The URLs listed below are the special ones that allow direct access to Privoxy. Of course, Privoxy must be running to access these. If not, you will get a friendly error message. Internet access is not necessary either.

- Privoxy main page:

  > http://config.privoxy.org/

  There is a shortcut: http://p.p/ (But it doesn't provide a fall-back to a real page, in case the request is not sent through Privoxy)

- Show information about the current configuration, including viewing and editing of actions files:

  > http://config.privoxy.org/show-status

- Show the source code version numbers:

  > http://config.privoxy.org/show-version

- Show the browser's request headers:

  > http://config.privoxy.org/show-request

- Show which actions apply to a URL and why:

  > http://config.privoxy.org/show-url-info

- Toggle Privoxy on or off. In this case, Privoxy continues to run, but only as a pass-through proxy, with no actions taking place:

  > http://config.privoxy.org/toggle

  Short cuts. Turn off, then on:

  > http://config.privoxy.org/toggle?set=disable

  > http://config.privoxy.org/toggle?set=enable

These may be bookmarked for quick reference. See next.

#### Bookmarklets

Below are some bookmarklets to allow you to easily access a mini version of some of Privoxy's special pages. They are designed for MS Internet Explorer, but should work equally well in Netscape, Mozilla, and other browsers which support JavaScript. They are designed to run directly from your bookmarks - not by clicking the links below (although that should work for testing).

To save them, right-click the link and choose Add to Favorites (IE) or Add Bookmark (Netscape). You will get a warning that the bookmark may not be safe - just click OK. Then you can run the Bookmarklet directly from your favorites/bookmarks. For even faster access, you can put them on the Links bar (IE) or the Personal Toolbar (Netscape), and run them with a single click.

- Privoxy - Enable

- Privoxy - Disable

- Privoxy - Toggle Privoxy (Toggles between enabled and disabled)

- Privoxy- View Status

- Privoxy - Submit Actions File Feedback

- Privoxy - Why?

Credit: The site which gave us the general idea for these bookmarklets is www.bookmarklets.com. They have more information about bookmarklets.

### Chain of Events

Let's take a quick look at the basic sequence of events when a web page is requested by your browser and Privoxy is on duty:

- First, your web browser requests a web page. The browser knows to send the request to Privoxy, which will in turn, relay the request to the remote web server after passing the following tests:

- Privoxy traps any request for its own internal CGI pages (e.g http://p.p/) and sends the CGI page back to the browser.

- Next, Privoxy checks to see if the URL matches any +block patterns. If so, the URL is then blocked, and the remote web server will not be contacted. +handle-as-image is then checked and if it does not match, an HTML BLOCKED page is sent back. Otherwise, if it does match, an image is returned. The type of image depends on the setting of +set-image-blocker (blank, checkerboard pattern, or an HTTP redirect to an image elsewhere).

- Untrusted URLs are blocked. If URLs are being added to the `trust` file, then that is done.

- If the URL pattern matches the +fast-redirects action, it is then processed. Unwanted parts of the requested URL are stripped.

- Now the rest of the client browser's request headers are processed. If any of these match any of the relevant actions (e.g. +hide-user-agent, etc.), headers are suppressed or forged as determined by these actions and their parameters.

- Now the web server starts sending its response back (i.e. typically a web page and related data).

- First, the server headers are read and processed to determine, among other things, the MIME type (document type) and encoding. The headers are then filtered as determined by the +crunch-incoming-cookies, +session-cookies-only, and +downgrade-http-version actions.

- If the +kill-popups action applies, and it is an HTML or JavaScript document, the popup-code in the response is filtered on-the-fly as it is received.

- If a +filter or +deanimate-gifs action applies (and the document type fits the action), the rest of the page is read into memory (up to a configurable limit). Then the filter rules (from `default.filter`) are processed against the buffered content. Filters are applied in the order they are specified in the `default.filter` file. Animated GIFs, if present, are reduced to either the first or last frame, depending on the action setting.The entire page, which is now filtered, is then sent by Privoxy back to your browser.

  If neither +filter or +deanimate-gifs matches, then Privoxy passes the raw data through to the client browser as it becomes available.

- As the browser receives the now (probably filtered) page content, it reads and then requests any URLs that may be embedded within the page source, e.g. ad images, stylesheets, JavaScript, other HTML documents (e.g. frames), sounds, etc. For each of these objects, the browser issues a new request. And each such request is in turn processed as above. Note that a complex web page may have many such embedded URLs.

### Anatomy of an Action

The way Privoxy applies actions and filters to any given URL can be complex, and not always so easy to understand what is happening. And sometimes we need to be able to see just what Privoxy is doing. Especially, if something Privoxy is doing is causing us a problem inadvertently. It can be a little daunting to look at the actions and filters files themselves, since they tend to be filled with regular expressions whose consequences are not always so obvious.

One quick test to see if Privoxy is causing a problem or not, is to disable it temporarily. This should be the first troubleshooting step. See the Bookmarklets section on a quick and easy way to do this (be sure to flush caches afterward!). Looking at the logs is a good idea too.

Privoxy also provides the http://config.privoxy.org/show-url-info page that can show us very specifically how actions are being applied to any given URL. This is a big help for troubleshooting.

First, enter one URL (or partial URL) at the prompt, and then Privoxy will tell us how the current configuration will handle it. This will not help with filtering effects (i.e. the +filter action) from the `default.filter` file since this is handled very differently and not so easy to trap! It also will not tell you about any other URLs that may be embedded within the URL you are testing. For instance, images such as ads are expressed as URLs within the raw page source of HTML pages. So you will only get info for the actual URL that is pasted into the prompt area -- not any sub-URLs. If you want to know about embedded URLs like ads, you will have to dig those out of the HTML source. Use your browser's View Page Source option for this. Or right click on the ad, and grab the URL.

Let's try an example, google.com, and look at it one section at a time:

     Matches for http://google.com:

     In file: default.action [ View ] [ Edit ]

    {-add-header
     -block
     -crunch-outgoing-cookies
     -crunch-incoming-cookies
     +deanimate-gifs{last}
     -downgrade-http-version
     +fast-redirects
     -filter{popups}
     -filter{fun}
     -filter{shockwave-flash}
     -filter{crude-parental}
     +filter{html-annoyances}
     +filter{js-annoyances}
     +filter{content-cookies}
     +filter{webbugs}
     +filter{refresh-tags}
     +filter{nimda}
     +filter{banners-by-size}
     +hide-forwarded-for-headers
     +hide-from-header{block}
     +hide-referer{forge}
     -hide-user-agent
     -handle-as-image
     -kill-popups
     -limit-connect
     +prevent-compression
     -send-vanilla-wafer
     -send-wafer
     +session-cookies-only
     +set-image-blocker{pattern} }
    /

     { -session-cookies-only }
     .google.com

     { -fast-redirects }
     .google.com

    In file: user.action [ View ] [ Edit ]
    (no matches in this file)

This tells us how we have defined our actions, and which ones match for our example, google.com. The first listing is any matches for the `standard.action` file. No hits at all here on standard. Then next is default, or our `default.action` file. The large, multi-line listing, is how the actions are set to match for all URLs, i.e. our default settings. If you look at your actions file, this would be the section just below the aliases section near the top. This will apply to all URLs as signified by the single forward slash at the end of the listing -- /.

But we can define additional actions that would be exceptions to these general rules, and then list specific URLs (or patterns) that these exceptions would apply to. Last match wins. Just below this then are two explicit matches for .google.com. The first is negating our previous cookie setting, which was for +session-cookies-only (i.e. not persistent). So we will allow persistent cookies for google. The second turns off any +fast-redirects action, allowing this to take place unmolested. Note that there is a leading dot here -- .google.com. This will match any hosts and sub-domains, in the google.com domain also, such as www.google.com. So, apparently, we have these two actions defined somewhere in the lower part of our `default.action` file, and google.com is referenced somewhere in these latter sections.

Then, for our `user.action` file, we again have no hits.

And finally we pull it all together in the bottom section and summarize how Privoxy is applying all its actions to google.com:

     Final results:

     -add-header
     -block
     -crunch-outgoing-cookies
     -crunch-incoming-cookies
     +deanimate-gifs{last}
     -downgrade-http-version
     -fast-redirects
     -filter{popups}
     -filter{fun}
     -filter{shockwave-flash}
     -filter{crude-parental}
     +filter{html-annoyances}
     +filter{js-annoyances}
     +filter{content-cookies}
     +filter{webbugs}
     +filter{refresh-tags}
     +filter{nimda}
     +filter{banners-by-size}
     +hide-forwarded-for-headers
     +hide-from-header{block}
     +hide-referer{forge}
     -hide-user-agent
     -handle-as-image
     -kill-popups
     -limit-connect
     +prevent-compression
     -send-vanilla-wafer
     -send-wafer
     -session-cookies-only
     +set-image-blocker{pattern}

Notice the only difference here to the previous listing, is to fast-redirects and session-cookies-only.

Now another example, ad.doubleclick.net:

     { +block +handle-as-image }
      .ad.doubleclick.net

     { +block +handle-as-image }
      ad*.

     { +block +handle-as-image }
      .doubleclick.net

We'll just show the interesting part here, the explicit matches. It is matched three different times. Each as an +block +handle-as-image, which is the expanded form of one of our aliases that had been defined as: +imageblock. (Aliases are defined in the first section of the actions file and typically used to combine more than one action.)

Any one of these would have done the trick and blocked this as an unwanted image. This is unnecessarily redundant since the last case effectively would also cover the first. No point in taking chances with these guys though ;-) Note that if you want an ad or obnoxious URL to be invisible, it should be defined as ad.doubleclick.net is done here -- as both a +block and an +handle-as-image. The custom alias +imageblock just simplifies the process and make it more readable.

One last example. Let's try http://www.rhapsodyk.net/adsl/HOWTO/. This one is giving us problems. We are getting a blank page. Hmmm ...

     Matches for http://www.rhapsodyk.net/adsl/HOWTO/:

     In file: default.action [ View ] [ Edit ]

     {-add-header
      -block
      -crunch-incoming-cookies
      -crunch-outgoing-cookies
      +deanimate-gifs
      -downgrade-http-version
      +fast-redirects
      +filter{html-annoyances}
      +filter{js-annoyances}
      +filter{kill-popups}
      +filter{webbugs}
      +filter{nimda}
      +filter{banners-by-size}
      +filter{hal}
      +filter{fun}
      +hide-forwarded-for-headers
      +hide-from-header{block}
      +hide-referer{forge}
      -hide-user-agent
      -handle-as-image
      +kill-popups
      +prevent-compression
      -send-vanilla-wafer
      -send-wafer
      +session-cookies-only
      +set-image-blocker{blank} }
       /

     { +block +handle-as-image }
      /ads

Ooops, the /adsl/ is matching /ads! But we did not want this at all! Now we see why we get the blank page. We could now add a new action below this that explicitly does not block ({-block}) paths with adsl. There are various ways to handle such exceptions. Example:

     { -block }
      /adsl

Now the page displays ;-) Be sure to flush your browser's caches when making such changes. Or, try using `Shift+Reload`.

But now what about a situation where we get no explicit matches like we did with:

     { +block +handle-as-image }
     /ads

That actually was very telling and pointed us quickly to where the problem was. If you don't get this kind of match, then it means one of the default rules in the first section is causing the problem. This would require some guesswork, and maybe a little trial and error to isolate the offending rule. One likely cause would be one of the {+filter} actions. These tend to be harder to troubleshoot. Try adding the URL for the site to one of aliases that turn off +filter:

     {shop}
     .quietpc.com
     .worldpay.com   # for quietpc.com
     .jungle.com
     .scan.co.uk
     .forbes.com

{shop} is an alias that expands to { -filter -session-cookies-only }. Or you could do your own exception to negate filtering:

     {-filter}
     .forbes.com

This would turn off all filtering for that site. This would probably be most appropriately put in `user.action`, for local site exceptions.

Images that are inexplicably being blocked, may well be hitting the +filter{banners-by-size} rule, which assumes that images of certain sizes are ad banners (works well most of the time since these tend to be standardized).

{fragile} is an alias that disables most actions. This can be used as a last resort for problem sites. Remember to flush caches! If this still does not work, you will have to go through the remaining actions one by one to find which one(s) is causing the problem.