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Tag extensions are extensions that extend the built-in wiki markup with Parser extension tags to provide additional capabilities ranging from simple string processing to full-blown information retrieval. For example, one might want to create a tag extension to introduce a simple ‎<donation /> tag that injects a donation form into the page.

Before you start work on a tag extension, you should always check to make sure someone else hasn't done exactly what you are trying to do. Also consider creating a parser function as an alternative to creating a parser tag.

A simple tag extension implements a callback function, which is hooked to the parser so that, when the parser runs, it will find and replace all instances of a specific tag, calling the corresponding callback function to render the actual HTML.

Parts of this page (those related to Section) are outdated. It was written for an older version of MediaWiki and may not apply to the most recent version. If you have checked or updated this page and found the content to be suitable, please remove this notice. See the talk page for a possible discussion on this.

In extension.json , set up the hooks:

...
  "Hooks": {
       "ParserFirstCallInit": "ExampleExtensionHooks"
   },
   "HookHandlers": {
       "ExampleExtensionHooks": {
           "class": "MediaWiki\\Extension\\ExampleExtension\\Hooks"
       }
   }
...

And add the hook into a PHP file

<?php
namespace MediaWiki\Extension\ExampleExtension;

class ExampleExtension implements ParserFirstCallInitHook {
	// Register any render callbacks with the parser
	public function onParserFirstCallInit( $parser ) {
		// When the parser sees the <sample> tag, it executes renderTagSample (see below)
		$parser->setHook( 'sample', [ $this, 'renderTagSample' ] );
	}

	// Render <sample>
	public function renderTagSample( $input, array $args, Parser $parser, PPFrame $frame ) {
		// Nothing exciting here, just escape the user-provided input and throw it back out again (as example)
		return htmlspecialchars( $input );
	}
}

This example registers a callback function for the ‎<sample> tag. When a user adds this tag to a page like this: <sample arg1="xxx" arg2="xxx">...input...</sample>, the parser will call the renderTagSample() function, passing in four arguments:

$input

Input between the ‎<sample> and ‎</sample> tags, or null if the tag is "closed", i.e. ‎<sample />

$args

Tag arguments, which are entered like HTML tag attributes; this is an associative array indexed by attribute name.

$parser

The parent parser (a Parser object); more advanced extensions use this to obtain the contextual Title, parse wiki text, expand braces, register link relationships and dependencies, etc.

$frame

The parent frame (a PPFrame object). This is used together with $parser to provide the parser with more complete information on the context in which the extension was called.

For a more elaborate example, see Tag extension example

Let's look at another example:

<?php

$wgHooks['ParserFirstCallInit'][] = 'onParserFirstCallInit';

function onParserFirstCallInit( Parser $parser ) {
	$parser->setHook( 'sample', 'wfSampleRender' );
}

function wfSampleRender( $input, array $args, Parser $parser, PPFrame $frame ) {
	$attr = [];    
	// This time, make a list of attributes and their values, and dump them, along with the user input
	foreach( $args as $name => $value ) {
		$attr[] = '<strong>' . htmlspecialchars( $name ) . '</strong> = ' . htmlspecialchars( $value );
	}
	return implode( '<br />', $attr ) . "\n\n" . htmlspecialchars( $input );

/**
 * The following lines can be used to get the variable values directly:
 * $to = $args['to'] ;
 * $email = $args['email'] ;
 */
}

This example dumps the attributes passed to the tag, along with their values. It's quite evident that this allows for flexible specification of new, custom tags. You might, for example, define a tag extension that allows a user to inject a contact form on their user page, using something like <emailform to="User" email="[email protected]" />.

There is a veritable plethora of tag extensions available for MediaWiki, some of which are listed on this site; others can be found via a quick web search. While a number of these are quite specialised for their use case, there are a great deal of well-loved and well-used extensions providing varying degrees of functionality.

See Manual:Developing extensions for the general layout and setup of an extension.

It has been suggested that this page or section be merged with Manual:Developing extensions#Deploying and registering#Publishing.(Discuss)

1. Create a new page on this wiki named Extension:<extension_name> with information on your extension, how to install it, and screenshots of it in use. A convenient template has been created to hold this information called Template:Extension . See the template page for more information. You should also add as much detail as possible to the body of the page, and it is wise to check back fairly regularly to respond to user questions on the associated talk page. Also, make sure the page belongs to Category:Extensions .
2. Extensions that create new hooks within the extension code should register them in the extension hook category.
3. Notify the mediawiki-l mailing list.

See also publishing your extension.

You'll notice above that the input in the examples above is escaped using htmlspecialchars() before being returned. It is vital that all user input is treated in this manner before echoing it back to the clients, to avoid introducing vectors for arbitrary HTML injection, which can lead to cross-site scripting vulnerabilities.

Your extension should add modules by attaching them to the ParserOutput. The module list will be taken from the ParserOutput object and added to the OutputPage, even when the page rendering is pre-cached. If you are adding the modules directly to the OutputPage they might not be cached in the parser output.

public function renderTagSample( $input, array $args, Parser $parser, PPFrame $frame ) {
	// ... do stuff ...
	$parser->getOutput()->addModules( 'ext.ExampleExtension' );
	$parser->getOutput()->addModuleStyles( 'ext.ExampleExtension.styles' );
	// ... do more stuff ...
}

If you change the code for an extension, all pages that use the extension will, theoretically, immediately reflect the results of new code. Technically speaking, this means your code is executed each and every time a page containing the extension is rendered.

In practice, this is often not the case, due to page caching - either by the MediaWiki software, the browser or by an intermediary proxy or firewall.

To bypass MediaWiki's parser cache and ensure a new version of the page is generated, click on edit, replace "action=edit" in the URL shown in the address bar of your browser by "action=purge" and submit the new URL. The page and all templates it references will be regenerated, ignoring all cached data. The purge action is needed if the main page itself is not modified, but the way it must be rendered has changed (the extension was modified, or only a referenced template was modified).

If this is not sufficient to get you a fresh copy of the page, you can normally bypass intermediary caches by adding '&rand=somerandomtext' to the end of the above URL. Make sure 'somerandomtext' is different every time.

Since MediaWiki 1.5, the parser is passed as the third parameter to an extension. This parser can be used to invalidate the parser cache like this:

function wfSampleSomeHookFunction( $text, array $args, Parser $parser, PPFrame $frame ) {
	$parser->getOutput()->updateCacheExpiry(0);
	// ...
}

Maybe you don't want to disable caching entirely, you just want the page to be regenerated whenever another page is edited, similar to the way that template transclusions are handled. This can be done using the parser object that is passed to your hook function and calling the addTemplate.

You can use fine grained caching for your extension by using cache keys to differentiate between different versions of your extension output. While rendering you can add cache keys for every feature by adding an addExtraKey method to your hook function, e.g.:

function wfSampleSomeHookFunction( $text, array $args, Parser $parser, PPFrame $frame ) {
	$userOptionsLookup = MediaWikiServices::getInstance()->getUserOptionsLookup();
	$setting1= (int)$userOptionsLookup->getOption( $parser->getUserIdentity(), 'setting1' );
	$parser->getOptions()->optionUsed( 'setting1' );
	$setting2= (int)$userOptionsLookup->getOption( $parser->getUserIdentity(), 'setting2' );
	$parser->getOptions()->optionUsed( 'setting2' );
	...
}

However, modifying $parser->getOptions() during parse means that the extra option keys aren't included when trying to get a cached page, only when rendering a page to go into cache, so you can use the PageRenderingHash hook to set extra options. PageRenderingHash is run both when putting a page into cache, and getting it out, so its important to only add new keys to the hash if they're not already there. e.g:

$wgHooks['PageRenderingHash'][] = 'wfMyExtOnPageRenderingHash';

function wfMyExtOnPageRenderingHash( &$confstr, $user, $optionsUsed ) {
	$userOptionsLookup = MediaWikiServices::getInstance()->getUserOptionsLookup();
	if ( in_array( 'setting1', $optionsUsed ) ) {
		$confstr .= "!setting1=" . $userOptionsLookup->getOption( $user, 'setting1' );
	}
	if ( in_array( 'setting2', $optionsUsed ) ) {
		$confstr .= "!setting2=" . $userOptionsLookup->getOption( $user, 'setting2' );
	}
}

Some important notes on this:

• Using "!setting1=$value" instead of just "!$value" in the confstr ensures that the parser cache does not become messed up if different extensions are installed or their load order changes. ! is used a separator for different rendering options
• Some people use $parser->getOptions()->addExtraKey() instead of $parser->getOptions()->optionUsed(). Be warned that addExtraKey does not tell the parser cache that the extra key is in use, and thus can easily result in breaking the cache if you are not careful.

Parser hook functions are passed a reference to the parser object and a frame object; these should be used to parse wikitext.

function wfSampleWonderfulHook( $text, array $args, Parser $parser, PPFrame $frame ) {
	$output = $parser->recursiveTagParse( $text, $frame );
	return '<div class="wonderful">' . $output . '</div>';
}

Parser::recursiveTagParse() has been around since version 1.8. Its advantages include simplicity (it takes just one argument and returns a string) and the fact that it parses extension tags in $text, so you can nest extension tags.

The second parameter to recursiveTagParse, $frame, is an optional argument introduced in MW 1.16 alpha (r55682).

• If $frame is provided (using the value of $frame passed to your extension), then any template parameters in $text will be expanded. In other words, content such as {{{1}}} will be recognized and converted into the appropriate value.
• If $frame is not provided (e.g., $parser->recursiveTagParse( $text )), or if $frame is set to false, then template parameters will not be expanded; {{{1}}} will not be altered. Although this unlikely to be the desired behavior, this was the only option available before MW 1.16.

However, one step of parsing that is still skipped for tags, even when using recursiveTagParse, is Parser::preSaveTransform. preSaveTransform is the first step of parsing, responsible for making permanent changes to the about-to-be saved wikitext, such as:

• Converting signatures (~~~, ~~~~, ~~~~~)
• Expanding link labels, also known as the pipe-trick (e.g., changing [[Help:Contents|]] into [[Help:Contents|Contents]]). Without this step, shorthand links such as [[Help:Contents|]] are considered to be invalid, and are left in their wikitext form when parsed.
• Expanding {{subst:}} templates.

The original call to preSaveTransform intentionally skips such conversions within all extension tags. If you need pre save transform to be done, you should consider using a parser function instead. All tag extensions can also be called as a parser function using {{#tag:tagname|input|attribute_name=value}} which will have pre save transform applied.

Since MediaWiki 1.5, XML-style parameters (tag attributes) are supported. The parameters are passed as the second parameter to the hook function, as an associative array. The value strings have already had HTML character entities decoded for you, so if you emit them back to HTML, don't forget to use htmlspecialchars( $codeToEncode, ENT_QUOTES ), to avoid the risk of HTML injection.

The return value of a tag extension is considered almost parsed text, which means its not treated as pure html, but still modified slightly. There are two main things that are done to the output of a tag extension (Along with a couple other minor things):

• Replace strip markers. Strip markers are certain items which are inserted at various stages of processing wikitext to act as a marker to re-insert removed content at a later time. This is not something extensions usually need to worry about.
• Parser::doBlockLevels which turns *'s into lists, and turns any line starting with a leading space into a ‎<pre> among other things. This can sometimes be an issue in some extensions.

Tag extensions also support returning an array instead of just a string (Much like parser functions) in order to change how the return value is interpreted. The 0th value of the array must be the HTML. The "markerType" key can be set to nowiki in order to stop further parsing. Doing something like return [ $html, 'markerType' => 'nowiki' ]; would ensure that the $html value is not further modified and treated as just plain html.

See Manual:Extension registration and register your extension accordingly.

Suppose you have several tags ‎<foo> and ‎<bar> that share the same callback, and inside the callback function, you want to obtain the name of the tag that invoked the callback.

$wgHooks['ParserFirstCallInit'][] = 'onParserFirstCallInit';

# ...

public function onParserFirstCallInit( Parser $parser ) {
	$parser->setHook( 'foo', 'sharedFunctionality' );
	$parser->setHook( 'bar', 'sharedFunctionality' );
}

# ...

public function sharedFunctionality( $input, array $args, Parser $parser, PPFrame $frame ) {
	// How to distinguish between 'foo' and 'bar' calls?
}

The short answer is: the tag name (foo or bar) is not present in any of the callback's arguments. But you can work around this by dynamically constructing a separate callback for each tag:

$wgHooks['ParserFirstCallInit'][] = 'onParserFirstCallInit';

# ...

public function onParserFirstCallInit( Parser $parser ) {
	// For each tag name
	foreach ( [ 'foo', 'bar' ] as $tagName ) {
		// Dynamically create a callback function
		$callback = function( $input, $args, $parser, $frame ) use ( $tagName ) {
			// The callback invokes the shared function.
			// Notice we now pass the tag name as a parameter.
			return sharedFunctionality( $input, $args, $parser, $frame, $tagName );
		};
		// Assign the callback to the tag
		$parser->setHook( $tagName, $callback );
	}
}

# ...

public function sharedFunctionality( $input, array $args, Parser $parser, PPFrame $frame, $tagName) {
	// Now we can retrieve the tag name and perform custom actions for that tag
	switch ( $tagName ) {
		//...
	}
}

Extension:WikiEditor provides an editing toolbar, allowing users to add tags into their editor by simply clicking a button. If you want a toolbar button for your new tag, create a file named something like toolbar-button.js in your extension's resources folder. The file should look like this:

var customizeToolbar = function () {
    $('#wpTextbox1').wikiEditor('addToToolbar', {
        section: 'main',
        group: 'format',
        tools: {
            "ExtensionName": { // replace with the name of your extension
                label: 'TagName', // replace with the label that should appear when hoving the button
                type: 'button',
                icon: "extensions/ExtensionName/images/button-image.svg", // path to the image that should go on the button
                action: {
                    type: 'encapsulate',
                    options: {
                        pre: "<tagName>", // tags that get inserted when the button is clicked
                        post: "</tagName>"
                    }
                }
            }
        }
    });
};

/* Check if view is in edit mode and that the required modules are available. Then, customize the toolbar … */
if ( [ 'edit', 'submit' ].indexOf( mw.config.get( 'wgAction' ) ) !== -1 ) {
    mw.loader.using( 'user.options' ).then( function () {
        // This can be the string "0" if the user disabled the preference ([[phab:T54542#555387]])
        if ( mw.user.options.get( 'usebetatoolbar' ) == 1 ) {
            $.when(
                mw.loader.using( 'ext.wikiEditor' ), $.ready
            ).then( customizeToolbar );
        }
    } );
}

Further details about customizing this file can be found here. Once you've created the file, you need to register it with ResourceLoader so it will be delivered to visitors; this is done by editing your extension.json:

"Hooks": {
    "BeforePageDisplay": "ExtensionName::onBeforePageDisplay"
}
"ResourceModules": {
    "ext.ExtensionName": {
        "scripts": ["toolbarButton.js"]
    }
}

Then, in your PHP file:

public static function onBeforePageDisplay( OutputPage $out ) {
    $out->addModules( [ 'ext.ExtensionName' ] );
}

• Help:Magic words – List of special tag/variables like {{PAGENAME}}, {{SERVER}}, ...
• Parser extension tags – List of parser tags in use on Wikimedia wikis.
• Manual:Extensions
• Extensions FAQ
• Category:Extensions
• Manual:$wgExtensionFunctions

• Outdated pages
• Pages to be merged
• Customization techniques
• MediaWiki development
• Parser extensions
• Sample code