This guide is aimed at filter authors and advanced users that want to make the most out of Adblock Plus. It's a companion to the guide on writing filters that covers snippet filters. While it's recommended that you be familiar with writing filters, you should be OK otherwise. You don't need a deep knowledge of JavaScript, but you need to be familiar with it, as well as with web technologies like HTML, CSS, and the DOM. If you really want, Mozilla has a great resource to learn JavaScript, HTML and CSS. 

This guide doesn't cover how to write an actual snippet, i.e. the JavaScript code that is loaded by Adblock Plus into the browser when you execute a snippet filter. This requires modifying the extension, and it will be covered in an upcoming developer guide.

Table of contents

• What are snippet filters?
• Syntax
• Arguments
• Examples
• Debugging
• Behavioral Snippets
• Conditional Hiding Snippets

What are snippet filters?

Snippet filters are a new type of filter introduced in Adblock Plus 3.3 that allows running specialized code snippets (written in JavaScript) on pages within a list of specified domains. These snippets are selected from an existing library available in Adblock Plus.

The snippet approach allows interfering with ad display code in a more efficient manner, and also allows locating elements to hide in a way that can't be expressed with CSS or the current advanced selectors.

For security reasons, snippet filters can only be added to a user's custom filters list or in the ABP Anti-Circumvention Filter List, the latter being vetted and reviewed.

Syntax

The basic syntax of a snippet filter is as follows:

You can run several snippets in the same filter by separating them with a ;. See example 6.

Arguments

Arguments are strings. They can be surrounded by single quotes (') if they contain spaces. To have a single quote ' as part of the argument, escape it like this: \' ; you can also escape spaces with \ instead of quoting the argument. See examples 3a, 3b and 3c.

You can input Unicode characters by using the syntax \uNNNN, where NNNN is the Unicode codepoint. See example 4.

You can also input carriage return, line feed, and tabs using \r, \n, and \t, respectively. To have a \ in an argument, including a regular expression, it must be escaped with \, i.e. doubled up. See example 5.

Examples

Basic snippet filter syntax

These examples demonstrate the syntax of a snippet filter and how to pass arguments. While we mostly use the log snippet, these examples apply to other snippet functions as well.

Example 1

example.com#$#log Hello

This prints "Hello" in the web console on the domain example.com and its subdomains.

Example 2

anotherexample.com,example.com#$#log Hello

Same as example 1, but "Hello" also appears on the domain anotherexample.com. Like with other filter types, multiple domains should be separated by commas ,.

This filter makes the filter in example 1 obsolete. Having both filters makes the message appear twice on example.com, as both would be run.

Example 3a

example.net,example.com#$#log 'Hello from an example to another example'

This is a different message from example 2. Because it contains spaces, the string must be surrounded with single quotes '.

Example 3b

example.net,example.com#$#log 'Hello it\'s me again'

This shows the escape sequence for having a single quote, using \'.

Example 3c

example.net,example.com#$#log Hello\ no\ quotes

You can also escape spaces instead of quoting the argument, using \.

Example 4

emoji.example.com#$#log \u1F601

On the domain emoji.example.com, the emoji 😀 is printed in the console. The filter will not be run on example.com or www.example.com. This shows how to use escape for Unicode symbols.

Example 5

emoji.example.com#$#log '\u1F601\nand a new line'

This is similar to example 4, except that the filter prints the emoji 😀 and then on a new line, prints and a new line. This shows how to use escape for Unicode symbols, as well as adding a new line.

Example 6

Running two snippets:

debug.example.com#$#debug; log 'This should be prefixed by DEBUG'

First, we see debug. This is the snippet that enables debugging. It's just like any other snippet. Then we see log, whose output is modified when debugging is enabled. See the section on debugging for more details.

example.com#$#log 'Always log'; log 'And better twice than once'

This is another example of logging two lines. Here the snippet command will be called twice.

Debugging

We saw a debug snippet in Example 6. Its use is simple: calling debug before a snippet turns on the debug flag. If the other snippets support it, they'll enable their debug mode. What a snippet does in debug mode is up to the snippet.

debug

Since: Adblock Plus 3.8

Enables debug mode.

Filter	Result
debug; log OK	logs OK to the console with a preceded by a DEBUG word
debug; abort-on-property-read atob	activates debug mode for the abort-on-property-read snippet

log

Since: Adblock Plus 3.3

Logs its arguments to the console. This may be used for testing and debugging.

Filter	Result
log OK	logs OK to the console
log Hello, world!	logs Hello, World! to the console (with 2 parameters)
log 'Hello, world!'	logs Hello, World! to the console (with 1 parameter)

trace

Since: Adblock Plus 3.3

Similar to log, but does the logging in the context of the document rather than the content script.

This may be used for testing and debugging, especially to verify that the injection of snippets into the document is working without any errors.

Filter	Result
trace OK	logs OK to the console
trace Hello, world!	logs Hello, World! to the console (with 2 parameters)
trace 'Hello, world!'	logs Hello, World! to the console (with 1 parameter)

Behavioral Snippets

abort-current-inline-script

Since: Adblock Plus 3.4.3

Aborts the execution of an inline script when a property is either read or written.

Name	Description	Mandatory
api	API function or property name to anchor on. It can also be the path to that property. If the property is a direct child of window, this parameter will be just the property name. But, if you want to access a sub property, this parameter will be a chain of properties separated by dots.	yes
search	If specified, only scripts containing the given string are prevented from executing. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	no

abort-on-property-read

Since: Adblock Plus 3.4.1

Patches a property on the window object to abort execution when the property is read.

No error is printed to the console.

The idea originates from uBlock Origin.

Name	Description	Mandatory
property	The name of the property or the path to that property. If the property is a direct child of window, this parameter will be just the property name. But, if you want to access a sub property, this parameter will be a chain of properties separated by dots.	yes
setConfigurable	Value of the configurable attribute of the descriptor of property. If this parameter is not used it defaults to true. Setting it to false will prevent the property set and get being overwritten or otherwise changed by anybody. If this snippet doesn't work as expected when passing only the property, it could mean that the website is circumventing and setting this parameter to false can come in handy.	no

abort-on-property-write

Since: Adblock Plus 3.4.3

Patches a property on the window object to abort execution when the property is written.

No error is printed to the console.

The idea originates from uBlock Origin.

Name	Description	Mandatory
property	The name of the property or the path to that property. If the property is a direct child of window, this parameter will be just the property name. But, if you want to access a sub property, this parameter will be a chain of properties separated by dots.	yes
setConfigurable	Value of the configurable attribute of the descriptor of property. If this parameter is not used it defaults to true. Setting it to false will prevent the property set and get being overwritten or otherwise changed by anybody. If this snippet doesn't work as expected when passing only the property, it could mean that the website is circumventing and setting this parameter to false can come in handy.	no

abort-on-iframe-property-read

Since: Adblock Plus 3.10.1

Patches a list of properties on the iframes' window object to abort execution when the property is read.

No error is printed to the console.

Name	Description
properties	The list with the properties we want to abort on.

abort-on-iframe-property-write

Since: Adblock Plus 3.10.1

Patches a list of properties on the iframes' window object to abort execution when the property is written.

No error is printed to the console.

Name	Description
properties	The list with the properties we want to abort on.

cookie-remover

Since: Adblock Plus 3.11.2

Name	Description	Mandatory
cookie	Pattern that matches the name of the cookie(s) we want to remove. If the string starts and ends with a slash (/), the text in between is treated as a regular expression.	yes
autoRemoveCookie	Default value:  false. When set to true, this parameter enables the snippet to continuously monitor the targeted cookie, checking for its presence every 1000 ms.  If the cookie is found, it will be repeatedly removed. To use only in case the website sets back the cookie after removal.	no

freeze-element

Since: Adblock Plus 3.10

Freezes a DOM element so it prevents adding new nodes inside it.

Name	Description	Example	Mandatory
selector	The CSS selector for the parent element that we want to freeze	'.left-content .container'	yes
options	A single parameter for snippet's options. A string containing all the options we want to pass, each of them separated by a plus character (+). Empty single quotes if none ('') Available options: •subtree (if we want to freeze all the element's children as well) •abort (throw an error every time an child element gets added)	'' or subtree or abort or subtree+abort etc.	no
exceptions	An array of regex/selectors used to specify the nodes we don't want to prevent being added. Each array item can be: •selector (targeting Element nodes) •regex (targeting Text nodes, identified by slash)	.article #banner .navigation /.*/	no

json-override

Since: Adblock Plus 3.11.2

It's very similar to json-prune, but instead of removing a property, we override it with a value from the same list as for override-property-read.

Name	Description	Mandatory
rawOverridePaths	A list of space-separated properties to remove. It also accepts property chains - e.g. foo.bar.tar.	yes
value	The value to override the property with (see below for possible values)	yes
rawNeedlePaths	A list of space-separated properties which must be all present for the pruning to occur. It also accepts property chains.	no
filter	A string to look for in the raw string, before it's passed to JSON.parse. If no match is found no further search is done on the resulting object. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	no

json-prune

Since: Adblock Plus 3.9.4

Overrides a property's value on the window object with a set of available properties.

The idea originates from uBlock Origin.

Name	Description	Mandatory
property	The name of the property or the path to that property. If the property is a direct child of window, this parameter will be just the property name. But, if you want to access a sub property, this parameter will be a chain of properties separated by dots.	yes
value	The value to override the property with.	yes
setConfigurable	Value of the configurable attribute of the descriptor of property. If this parameter is not used it defaults to true. Setting it to false will prevent the property set and get being overwritten or otherwise changed by anybody. If this snippet doesn't work as expected when passing only the property and the value, it could mean that the website is circumventing and setting this parameter to false can come in handy.	no

prevent-listener

Since: Adblock Plus 3.11.2

Prevents adding event listeners.

Wrap EventTarget.prototype.addEventListener and don't allow adding listeners for certain types of events.

Name	Description	Mandatory
type	Pattern that matches the type(s) of event we want to prevent. If the string starts and ends with a slash (/), the text in between is treated as a regular expression.	yes
handler	Pattern that matches the event handler's declaration. If the string starts and ends with a slash (/), the text in between is treated as a regular expression.	no
selector	The CSS selector that the event target must match. If the event target is not an HTML element the event handler is added.	no

simulate-event-poc [Deprecated]

Since: Adblock Plus 3.11.2

Triggers an event handler or a combination of those.

Name	Description	Mandatory
event	The event we want to dispatch.	yes
selector	The CSS/Xpath selector that an HTML element must match for the event to be triggered.	yes
delay	The delay between the moment when the node is inserted and the moment when the event is dispatched.	no

simulate-mouse-event

Since: Adblock Plus 3.17

Triggers arbitrary mouse events on elements that are matched by a CSS or Xpath selector, by calling dispatchEvent for a selector.

Name	Description	Mandatory
selectors	The CSS/Xpath selector that an HTML element must match for the event to be triggered. Maximum 7 selectors are supported. Take a look at the optional parameters and the examples below for the explanation of how they should be written.	yes

Optional parameters are added to the selectors with a $ sign. Multiple parameters can be combined for a single selector by separating them with a comma. If a parameter is not specified, the default value will be assumed for that selector.

Name	Description	Default	Mandatory
$trigger	If this flag is not set, only the chosen event for the last selector will be triggered. $trigger flag can be used for the other selectors to make sure the event is triggered for them as well. $trigger is always true for the last selector so can be omitted for it.	false	no
$delay	Determines how much time the snippet should wait before simulating the even. Note that the default is 500 ms. If you don't want to have a delay (same as in simulate-event-poc), you should explicitly state $delay=0.	500	no
$continue	If set, the event will be triggered after each delay period ends. For example, if the selected event is click and the delay is 500 ms. The click event will be triggered every 500 ms instead of just once.	false	no
$event	Determines which event should be simulated for the selector.	click	no

 

Filter	Result
simulate-mouse-event 'some-css-selector'	Simulates a click event for the eleents that match the selector after 500 ms.
simulate-mouse-event 'css-selector1' 'css-selector2'	Simulates a click event for css-selector2 only if the css-selector1 is present in the page. Does not click css-selector1.
simulate-mouse-event 'css-selector1$trigger' 'css-selector2'	Simulates a click event for both of the selectors if both of them are present in the page. Note that the $trigger parameter for css-selector2 can be omitted as it is the last parameter.
simulate-mouse-event 'xpath(some-xpath-selector)$delay=0'	Simulates a click event for the elements that are matched with the xpath selector with no delay. This is the same behaviour as simulate-event-poc.
simulate-mouse-event 'some-css-selector$continue,delay=100'	Simulates a click event every 100 ms.
simulate-mouse-event 'some-css-selector$continue,delay=100, event=mouseover'	Simulates a mouseover (hover) event over all the elements matching the selector every 100 ms.

As you can see the you can mix and match the parameters to create the filter that best suits the case. The parameters doesn't have any order $delay=100,trigger is the same as $trigger,delay=100. 

skip-video

Since: Adblock Plus 3.21

strip-fetch-query-parameter

Since: Adblock Plus 3.5.1

Strips a query string parameter from fetch() calls.

Name	Description	Mandatory
name	The name of the parameter.	yes
urlPattern	An optional pattern that the URL must match. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	no

Conditional Hiding Snippets

hide-if-contains

Since: Adblock Plus 3.3

Hides any HTML element or one of its ancestors matching a CSS selector if the text content of the element contains a given string.

Name	Description	Mandatory
search	The string to look for in HTML elements. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	yes
selector	The CSS selector that an HTML element must match for it to be hidden.	yes
searchSelector	The CSS selector that an HTML element containing the given string must match. Defaults to the value of the selector argument.	no

hide-if-contains-image

Since: Adblock Plus 3.4.2

Hides any HTML element or one of its ancestors matching a CSS selector if the background image of the element matches a given pattern.

Name	Description	Mandatory
search	The pattern to look for in the background images of HTML elements. This must be the hexadecimal representation of the image data for which to look. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	yes
selector	The CSS selector that an HTML element must match for it to be hidden.	yes
searchSelector	The CSS selector that an HTML element containing the given pattern must match. Defaults to the value of the selector argument.	no

hide-if-contains-similar-text

Since: Adblock Plus 3.14.2

Hides an element based on its similar text content.

hide-if-contains-similar-text currently uses a pre-sorted Levenshtein distance for cases where the content has shuffled chars or text.

Name	Description	Mandatory
search	The string to match to the similar text. Is considered similar text that isn't hidden by CSS properties or other means. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	yes
selector	The CSS selector that an HTML element must match for it to be hidden.	yes
searchSelector	The CSS selector that an HTML element containing the given string must match. Defaults to the value of the selector argument.	no

hide-if-contains-visible-text

Since: Adblock Plus 3.6

Hides any HTML element matching a CSS selector if the visible text content of the element contains a given string.

It can also check an unlimited amount of CSS attributes of a node to locate a specific string, even when a website employs methods to obscure or conceal the text.

Name	Description	Mandatory
search	The string to match to the visible text. Is considered visible text that isn't hidden by CSS properties or other means. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	yes
selector	The CSS selector that an HTML element must match for it to be hidden.	yes
searchSelector	The CSS selector that an HTML element containing the given string must match. Defaults to the value of the selector argument.	no
optionalParameters	You can provide any number of optional parameters. There are 2 kinds of optional parameters: [1] tuning text matching logic or [2] adding arbitrary CSS attributes. There are some circumvention techniques that might mess with the string matching logic. This snippets has logic that determines which text is visible and which is not. This logic can be tuned by overriding the default parameters (see table below). You can provide additional CSS rules to help filter out HTML elements, thereby minimizing false positives. These CSS attributes should align with the computed styles of the HTML elements responsible for obfuscating the <search> string. If the string you are attempting to match is not obfuscated, there's no need to include optional parameters. The snippet already verifies certain CSS values (as indicated in the table below). The optional parameters need to follow these syntax rules: <key>:<value>, where <value> can be a string or a regex (if it starts and ends with a `/`) each parameter is wrapped in single quotes, for example:'-snippet-box-margin:10px' 'width:0px'	no

Default Parameters
In order to tackle common circumvention patterns, the snippet checks already some styles in the matched element, even if you don't add any optional parameter. You can see the default values in the "Default value" column.

Note that you can override the default parameters by adding them as optional parameter, following the syntax rules explained above. You can give any value, the "How to overwrite" column shows only examples. Adjust the values according to your needs.

Name	Description	Default Value	How to overwrite
-check-is-contained	Used to categorize elements that are pushed outside of a parent even if the parent does not have the style overflow:hidden.	'-check-is-contained:false'	'-check-is-contained:true'
-disable-bg-color-check	Used to disable the check where we categorize elements with the same text color and background color as "not visible".	'-disable-bg-color-check:false'	'-disable-bg-color-check:true'
-snippet-box-margin	Used to expand the bounding box of the overflow parent. This is useful if the website is pushing some elements outside of a overflow:hidden parent. Unit is pixels.	'-snippet-box-margin:2'	'-snippet-box-margin:10'
color	Used to check if the gibberish text that scrambles the string we are looking is made invisible by the font color.	'color:rgba(0, 0, 0, 0)'	'color:rgba(255, 99, 71, 0.6)'
font-size	Used to check if the gibberish text that scrambles the string we are looking is made invisible by the font-size.	'font-size:0'	'font-size:16'
opacity	Used to check if the gibberish text that scrambles the string we are looking for is contained in a transparent element.	'opacity:0'	'opacity:1'

hide-if-contains-and-matches-style

Since: Adblock Plus 3.3.2

Hides any HTML element or one of its ancestors matching a CSS selector if the text content of the element contains a given string and, optionally, if the element's computed style contains a given string.

Name	Description	Mandatory
search	The string to look for in HTML elements. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	yes
selector	The CSS selector that an HTML element must match for it to be hidden.	yes
searchSelector	The CSS selector that an HTML element containing the given string must match. Defaults to the value of the selector argument.	no
style	The string that the computed style of an HTML element matching selector must contain. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	no
searchStyle	The string that the computed style of an HTML element matching searchSelector must contain. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	no
waitUntil	Optional parameter that can be used to delay the running of the snippet until the given state is reached. Accepts: loading, interactive, complete, load or any event name.	no
windowWidthMin	Optional parameter that can be used to disable the snippet if the window.innerWidth is smaller than the given value.	no
windowWidthMax	Optional parameter that can be used to disable the snippet if the window.innerWidth is greater than the given value.	no

hide-if-has-and-matches-style

Since: Adblock Plus 3.4.2

Hides any HTML element or one of its ancestors matching a CSS selector if a descendant of the element matches a given CSS selector and, optionally, if the element's computed style contains a given string.

Name	Description	Mandatory
search	The CSS selector against which to match the descendants of HTML elements.	yes
selector	The CSS selector that an HTML element must match for it to be hidden.	yes
searchSelector	The CSS selector that an HTML element containing the specified descendants must match. Defaults to the value of the selector argument.	no
style	The string that the computed style of an HTML element matching selector must contain. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	no
searchStyle	The string that the computed style of an HTML element matching searchSelector must contain. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	no
waitUntil	Optional parameter that can be used to delay the running of the snippet until the given state is reached. Accepts: loading, interactive, complete, load or any event name.	no
windowWidthMin	Optional parameter that can be used to disable the snippet if the window.innerWidth is smaller than the given value.	no
windowWidthMax	Optional parameter that can be used to disable the snippet if the window.innerWidth is greater than the given value.	no

hide-if-labelled-by

Since: Adblock Plus 3.9

Hides any HTML element that uses an aria-labelledby, or one of its ancestors, if the related aria element contains the searched text.

Name	Description	Mandatory
search	The string to look for in HTML elements. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	yes
selector	The CSS selector of an HTML element that uses as aria-labelledby attribute.	yes
searchSelector	The CSS selector of an ancestor of the HTML element that uses as aria-labelledby attribute. Defaults to the value of the selector argument.	no

hide-if-matches-computed-xpath

Since: Adblock Plus 3.18.1

Hide a specific element whose class name or id changes in runtime through a dynamically build XPath query.

This snippet takes as first parameter an incomplete XPath selector. Incomplete because it has a placeholder in form of {{}}. The next parameters, searchQuery and searchRegex, will tell the snippet how to fill the placeholder.

Name	Description	Mandatory
query	The template XPath query that targets the element to hide. Use {{}} to dynamically insert into the query.	yes
searchQuery	XPath query that searchs for an element to be used alongside searchRegex.	yes
searchRegex	The regex that is used to extract a text from the innerHTML of the element that matches searchQuery. The extracted text will be injected to the query.	yes
waitUntil	Optional parameter that can be used to delay the running of the snippet until the given state is reached. Accepts: loading, interactive, complete, load or any event name.	no

hide-if-matches-xpath

Since: Adblock Plus 3.9.0

Hide a specific element through a XPath 1.0 query string. See Getting started with XPath filters to know more.

Name	Description	Mandatory
query	The XPath query that targets the element to hide.	yes
scopeQuery	CSS or XPath selector that the filter devs can use to restrict the scope of the Mutation Observer. It is important that the selector is as specific as possible to avoid to match too many nodes.	no

hide-if-matches-xpath3

Since: Adblock Plus 3.19

Hides a specific element through a XPath 3.1 query string.

Name	Description	Mandatory
query	The XPath query that targets the element to hide.	yes
scopeQuery	CSS or XPath selector that the filter devs can use to restrict the scope of the Mutation Observer. It is important that the selector is as specific as possible to avoid to match too many nodes.	no

hide-if-shadow-contains

Since: Adblock Plus 3.3

Hides any HTML element or one of its ancestors matching a CSS selector if the text content of the element's shadow contains a given string.

Name	Description	Mandatory
search	The string to look for in every HTML element's shadow. If the string begins and ends with a slash (/), the text in between is treated as a regular expression.	yes
selector	The CSS selector that an HTML element must match for it to be hidden.	yes