Manual:Hooks

A hook is triggered by a call to HookContainer::run, usually via a method in HookRunner. HookContainer will find the hook handlers to run and call them with the parameters given to HookContainer::run. Hook handlers are registered via extension.json .

See also Hooks.md.

In this example from the doPurge function in WikiPage.php, doPurge calls HookRunner::onArticlePurge to run the ArticlePurge hook, passing $this as argument:

$this->getHookRunner()->onArticlePurge( $this )

The Core calls many hooks, but Extensions can also call hooks.

A hook handler is a function you register, which will be called whenever the hook in question is run.

For extensions, register your hook handlers in extension.json :

{
	"Hooks": {
		"EventName": [
			"MyExtensionHooks::onEventName",
			"someFunction"
		]
	}
}

Hook handlers can also be registered via the global $wgHooks array. This is most commonly used for site-specific customisations in LocalSettings.php, or in legacy extensions that predate extension.json. All the following are valid ways to define a hook handler for the EventName hook, with two parameters passed:

$wgHooks['EventName'][] = function ( $param1, $param2 ) {
// ...function body
};

Note that when an object is assigned, and you don't specify a method, the method called is "onEventName". For example "onArticleSave", "onUserLogin", etc.

The optional data is useful if you want to use the same function or object for different purposes. For example:

$wgHooks['PageContentSaveComplete'][] = [ 'efIrcNotify', 'TimStarling' ];
$wgHooks['PageContentSaveComplete'][] = [ 'efIrcNotify', 'brion' ];

This code would result in efIrcNotify() being run twice when a page is saved: once for 'TimStarling', and once for 'brion'.

Hooks fall into one of two categories, distinguished by the supported return values:

A void hook does not return anything. Void hook should be the most common kind in new code (T245364).

• Documentation: @return void
• Usage: $hookRunner->onExample();

The interface for void hooks must include a native return type hint like : void, so that extensions that choose to implement the interface (as opposed to handling it without interface validation), benefit from static analysis and thus avoid accidentally returning something. This prevents severe bugs that are hard to catch otherwise (T173615). These hooks ignore the return value and so in isolation, a return value is simply unused, harmless, with no visible effect. In production, it would cancel listeners from other extensions for the same hook. Effectively undeploying only part of an extension this way can have major consequences.

Abortable hooks may return boolean false. When a non-void return value is given to an abortable hook, it skips any and all other listeners for the same hook (i.e. in other extensions), and returns false to the hook caller. This is similar to Event.stopImmediatePropagation() and Event.preventDefault() in JavaScript.

If as the author of a feature, you want to allow an extension to disallow or cancel the user action, you can provide an abortable hook for this.

• Documentation: @return bool|void
• Usage: if ( $hookRunner->onExample() ) { … }

It is important that abortable hooks allow a void return. The majority of hook consumers do not make use of the abortable feature, and thus should be able to type their implementation to @return void and safely avoid the need to return something, and with it benefit from having no room for mistakingly returning false.

Return values:

• void (no return value, or null) - the hook handler finished successfully. (Before MediaWiki 1.23, returning true was required.)

• false - the hook handler has done all the work necessary, or replaced normal handling. This will prevent further handlers from being run, and in some cases tells the calling function to skip normal processing.

Prior to MediaWiki 1.41, abortable hooks could return an error message as string. This was a shortcut for producing an Internal Server Error (HTTP 500) response with the returned string displayed as the fatal error. This was deprecated in MW 1.35 (Gerrit change 571297), and removed in MW 1.41 (Gerrit change 571297).

MediaWiki 1.35 introduces the HookHandlers extension attribute. This includes per-hook interfaces for improved static validation and discovery of parameter documentation. It also enables dependency injection by introducing an intermediary class instance that accepts a number of specified services (instead of static callbacks that explicitly access services from global state).

The approach from MediaWiki 1.34 and earlier, of registering hook handlers directly as static methods, remains supported and is not deprecated. Extension authors may opt-in to the new system are welcome to do so. To learn more, see the MediaWiki core: Hook specification and the announcement on wikitech-l.

Prior to MediaWiki 1.35, hooks sometimes included characters that could not be used in a class or method name, such as colons and dashes. With the introduction of per-hook interfaces, the canonical names of these hooks have been changed to use underscores instead. For example, the interface for ApiFeedContributions::feedItem is ApiFeedContributions__feedItemHook. Hook handlers that are registered with the old names remain supported.

To adopt the new system, change your Hooks class to have regular methods instead of static methods and to be constructible. This class is then registered once, via the HookHandlers attribute in extension.json , using the class option as part of an ObjectFactory description where you can use the services option.

For example, to register the BeforePageDisplay hook:

{
    "HookHandlers": {
        "main": {
            "class": "MediaWiki\\Extension\\Example\\Hooks",
            "services": [ "UserNameUtils" ]
        }
    },
    "Hooks": {
        "BeforePageDisplay": "main"
    }
}

To use hook interfaces, extensions should define a Hooks class in their namespace and implement one or more hook interfaces. Hook interfaces are named with the hook name followed by the word "Hook".

namespace MediaWiki\Extension\MyExtension;

use MediaWiki\Hook\BeforePageDisplayHook;
use OutputPage;
use Skin;

class Hooks implements BeforePageDisplayHook {
    public function onBeforePageDisplay( $out, $skin ): void { ... }
}

Follow these steps for each hook handling method:

• identify the hook handler interface, and make the Hooks class implement this interface.
• update the method name and signature to be exactly the same as in the interface.
• change the Hooks section of extension.json to refer to the handler you specified in the HookHandlers section.

The process was demonstrated at the Wikimedia Hackathon 2021 :

• Example patch for an extension
• Recording on YouTube

Currently, hooks in MediaWiki core have to be documented both in hook interface (in the source code repository) and here on MediaWiki.org. In some cases, one of these steps may not yet have been completed, so if a hook appears undocumented, check both.

Each hook provided by MediaWiki Core is defined in a hook interface. Typically, hook interfaces are located in a "Hook" sub-namespace inside the caller namespace. For example, Storage/Hook/PageContentSaveHook.php. You can find a list of hook interfaces in the generated MediaWiki PHP documentation.

To document a hook on-wiki, use {{MediaWikiHook }}.

Hook interface doc template

In hook interfaces, doc comments specify the status, purpose, parameters, and behaviour of the hook.

/**
 * @stable for implementation
 * @ingroup Hooks
 */
interface MyExampleHook {
	/**
	 * This hook is called after/when...
	 * Use this hook to...
	 *
	 * @since x.xx
	 * @param string $name Description
	 * @return void This hook must not abort, it must return no value
	 */
	public function onMyExample( $name ): void;
}

/**
 * @stable for implementation
 * @ingroup Hooks
 */
interface AbortableExampleHook {
	/**
	 * This hook is called before...
	 * Use this hook to...
	 *
	 * @since x.xx
	 * @param string $name Description
	 * @@return bool|void True or no return value to continue or false to abort
	 */
	public function onAbortableExample( $name );
}

Some of these hooks can be grouped into multiple functions.

Sections: Article Management - Edit Page - Page Rendering - User Interface - File Management - Special Pages - User Management - Logging - Skinning Templates - API - Import/Export - Diffs - Miscellaneous

Warning:

New hooks are added to MediaWiki fairly frequently, so this list is not always completely up to date. As with most documentation on this site, if you need complete up-to-the-minute information you are advised to consult the generated list of hook interfaces. As ever, you are encouraged to update this list to correct any errors or omissions.

For a complete list of hooks, use the category , which should be kept more up to date.

• $wgHooks
• Category:Hook extensions
• Manual:Tag extensions
• Manual:Parser functions
• Hooks.md — specification of the hooks system
• List of hook interfaces in MediaWiki Core
• Extension:Examples — contains examples of hooks
• mw.hook — the JavaScript/front-end system of hooks