Manual:Developing extensions

Each [[<tvar name=man>Special:MyLanguage/Manual:Extensions</tvar>|extension]] consists of three parts:

1. Setup
2. Execution
3. Localisation

A minimal extension will consist of the following structure:

MyExtension/extension.json

Stores the [[<tvar name=setup>#Setup</tvar>|setup]] instructions. The file name must be extension.json. (Prior to MediaWiki 1.25 the setup instructions were in a <tvar name=php>MyExtension/MyExtension.php</tvar> file named after the extension. Many extensions still have backwards-compatibility shims in this PHP file.)

MyExtension/includes/ (or MyExtension/src/)

Stores the PHP [[<tvar name=execution>#Execution</tvar>|execution]] code for the extension.

MyExtension/resources/ (or MyExtension/modules/)

Stores the client-side resources such as JavaScript, CSS and LESS for the extension.

MyExtension/i18n/*.json

Stores [[<tvar name=localisation>#Localisation</tvar>|localisation]] information for the extension.

When you develop an extension, replace <tvar name=1>MyExtension</tvar> above with the name of your extension.
Use UpperCamelCase names for its directory and PHP file(s); this is the general [[<tvar name=1>Special:MyLanguage/Manual:Coding conventions#File naming</tvar>|file naming]] convention.
(The {{<tvar name=git-repo>git repo|project=mediawiki/extensions/BoilerPlate</tvar>|text=BoilerPlate extension}} is a good starting point for your extension.)

While developing, you may want to disable caching by setting <tvar name=code1> = CACHE_NONE</tvar> and <tvar name=code2> = false</tvar>, otherwise system messages and other changes may not show up.

Setup

Your goal in writing the setup portion is to make installing the extension as easy as possible, so users only have to add this line to <tvar name=1>LocalSettings.php</tvar>:

wfLoadExtension( 'MyExtension' );

If you want to make your extension user configurable, you need to define and document some configuration parameters and your users' setup should look something like this:

wfLoadExtension( 'MyExtension' );
$wgMyExtensionConfigThis = 1;
$wgMyExtensionConfigThat = false;

To reach this simplicity, your setup file needs to accomplish a number of tasks (described in detail in the following sections):

• register any media handler, [[<tvar name=2>Special:MyLanguage/Manual:Parser functions</tvar>|parser function]], [[<tvar name=5>Special:MyLanguage/Manual:Special pages</tvar>|special page]], [[<tvar name=3>Special:MyLanguage/Manual:Tag extensions</tvar>|custom XML tag]], and [[<tvar name=4>Special:MyLanguage/Manual:Variable</tvar>|variable]] used by your extension.

• define and/or validate any configuration variables you have defined for your extension.

• prepare the classes used by your extension for autoloading

• determine what parts of your setup should be done immediately and what needs to be deferred until the MediaWiki core has been initialized and configured

• define any additional [[<tvar name=man>Special:MyLanguage/Manual:Hooks</tvar>|hooks]] needed by your extension

• create or check any new database tables required by your extension.

• set up localisation for your extension

Good practice is to add a <tvar name=1>README</tvar> file with basic info about how to install and configure the extension. You can use either plain text or [<tvar name=url>https://secure.phabricator.com/book/phabricator/article/remarkup/</tvar> Phabricator markup syntax]. For example, see the [<tvar name=url>https://phabricator.wikimedia.org/diffusion/EPFM</tvar> Phabricator Diffusion page] for the <tvar name=1></tvar>. If markdown is used, add the file extension <tvar name="1">.md</tvar>. For example, see the <tvar name=1>README.md</tvar> file for <tvar name=2></tvar> on [<tvar name=url>https://phabricator.wikimedia.org/diffusion/GPAR</tvar> Phabricator Diffusion].

Registering features with MediaWiki

MediaWiki lists all the extensions that have been installed on its <tvar name=Version>Special:Version</tvar> page.
For example, you can see all the extensions installed on this wiki at <tvar name=Version>Special:Version</tvar>.

To do this, add the extension details to <tvar name=1>'</tvar>.
The entry will look something like this:

{
	"name": "Example",
	"author": "John Doe",
	"url": "https://www.mediawiki.org/wiki/Extension:Example",
	"description": "This extension is an example and performs no discernible function",
	"version": "1.5",
	"license-name": "GPL-2.0-or-later",
	"type": "validextensionclass",
	"manifest_version": 1
}

Many of the fields are optional, but it's still good practice to fill them out.
The manifest_version refers to the version of the schema the <tvar name=json></tvar> file is written against.
The available versions are 1 and 2. See [[<tvar name=1>Special:MyLanguage/Manual:Extension.json/Schema#manifest version</tvar>|here for the documentation on this feature]].
Unless you need to support an older version of MediaWiki, pick the latest version.

In addition to the above registration, you must also "hook" your feature into MediaWiki.
The above only sets up the Special:Version page.
The way you do this depends on [[<tvar name=1>#Extension types</tvar>|the type of your extension]].
For details, please see the documentation for each type of extension:

Making your extension user configurable

If you want your user to be able to configure your extension, you'll need to provide one or more configuration variables.
It is a good idea to give those variables a unique name.
They should also follow MediaWiki [[<tvar name=man>Special:MyLanguage/Manual:Coding conventions/PHP#Naming</tvar>|naming conventions]] (e.g. global variables should begin with $wg).

For example, if your extension is named "MyExtension", you might want to name all your configuration variables to begin with $wgMyExtension.
It is important that none of the MediaWiki core begins its variables this way and you have done a reasonable job of checking to see that none of the published extensions begin their variables this way.
Users won't take kindly to having to choose between your extension and some other extensions because you chose overlapping variable names.

It is also a good idea to include extensive documentation of any configuration variables in your installation notes.

Here is an example boiler plate that can be used to get started:

{
	"name": "BoilerPlate",
	"version": "0.0.0",
	"author": [
		"Your Name"
	],
	"url": "https://www.mediawiki.org/wiki/Extension:BoilerPlate",
	"descriptionmsg": "boilerplate-desc",
	"license-name": "GPL-2.0-or-later",
	"type": "other",
	"AutoloadClasses": {
		"BoilerPlateHooks": "includes/BoilerPlateHooks.php",
		"SpecialHelloWorld": "includes/SpecialHelloWorld.php"
	},
	"config": {
		"BoilerPlateEnableFoo": {
			"value": true,
			"description": "Enables the foo functionality"
		}
	},
	"callback": "BoilerPlateHooks::onExtensionLoad",
	"ExtensionMessagesFiles": {
		"BoilerPlateAlias": "BoilerPlate.i18n.alias.php"
	},
	"Hooks": {
		"NameOfHook": "BoilerPlateHooks::onNameOfHook"
	},
	"MessagesDirs": {
		"BoilerPlate": [
			"i18n"
		]
	},
	"ResourceModules": {
		"ext.boilerPlate.foo": {
			"scripts": [
				"resources/ext.boilerPlate.js",
				"resources/ext.boilerPlate.foo.js"
			],
			"styles": [
				"resources/ext.boilerPlate.foo.css"
			]
		}
	},
	"ResourceFileModulePaths": {
		"localBasePath": "",
		"remoteExtPath": "BoilerPlate"
	},
	"SpecialPages": {
		"HelloWorld": "SpecialHelloWorld"
	},
	"manifest_version": 2
}

Note that after calling <tvar name=1>wfLoadExtension( 'BoilerPlate' );</tvar> the global variable <tvar name=2>$wgBoilerPlateEnableFoo</tvar> does not exist.
If you set the variable, e.g. in <tvar name="1">LocalSettings.php</tvar> then the default value given in extension.json will not be used.

For more details on how to use global variable inside custom extensions, please refer to <tvar name=1></tvar>.

Preparing classes for autoloading

If you choose to use classes to implement your extension, MediaWiki provides a simplified mechanism for helping PHP find the source file where your class is located.
In most cases this should eliminate the need to write your own <tvar name=autoload>__autoload($classname)</tvar> method.

To use MediaWiki's autoloading mechanism, you add entries to the <tvar name=AutoloadClasses></tvar> field.
The key of each entry is the class name; the value is the file that stores the definition of the class.
For a simple one class extension, the class is usually given the same name as the extension, so your autoloading section might look like this (extension is named <tvar name=1>MyExtension</tvar>):

{
	"AutoloadClasses": {
		"MyExtension": "includes/MyExtension.php"
	}
}

The filename is relative to the directory the extension.json file is in.

For more complex extensions, [<tvar name=1>https://php.net/language.namespaces</tvar> namespaces] should be considered.
See [[<tvar name=1>Special:MyLanguage/Manual:Extension.json/Schema#AutoloadNamespaces</tvar>|Manual:Extension.json/Schema#AutoloadNamespaces]] for details.

Defining additional hooks

See <tvar name=1></tvar>.

Adding database tables

Make sure the extension doesn't modify the core database tables.
Instead, extension should create new tables with foreign keys to the relevant MW tables.  

File:OOjs UI icon notice-destructive.svg <translate> Warning:</translate>

If your extension is used on any production WMF-hosted wiki please follow the [<tvar name=url>https://wikitech.wikimedia.org/wiki/Schema_changes</tvar> Schema change guide].

If your extension needs to add its own database tables, use the <tvar name=LoadExtensionSchemaUpdates></tvar> hook.
See the manual page for more information on usage.

Set up localisation

See:

• Localisation (summary)

Add logs

On MediaWiki, all actions by users on wiki are tracked for transparency and collaboration.
See <tvar name=1></tvar> for how to do it.

Handling dependencies

Assume that an extension requires the presence of another extension, for example because functionalities or database tables are to be used and error messages are to be avoided in case of non-existence.

For example the extension <tvar name=1></tvar> requires the presence of the extension <tvar name=2></tvar> for certain functions.

One way to specify this would be by using the [[<tvar name=1>Special:MyLanguage/Manual:Extension.json/Schema#requires</tvar>|requires]] key in [[<tvar name=2>Special:MyLanguage/Manual:Extension.json</tvar>|extension.json]].

Another option is using ExtensionRegistry (available since MW 1.25):

	if ( ExtensionRegistry::getInstance()->isLoaded( 'HitCounters', '>=1.1' ) {
		/* do some extra stuff, if extension HitCounters is present in version 1.1 and above */
	}

Currently (as of February 2024, MediaWiki 1.41.0) the name of the extension-to-be-checked needs to exactly match the name in their extension.json.

Example: if you want to check the load status of extension "OpenIDConnect", you have to use it with a space

	if ( ExtensionRegistry::getInstance()->isLoaded( 'OpenID Connect' ) {
    ...
	}

Localisation

While developing, you may want to disable both cache by setting <tvar name=code1>$wgMainCacheType = CACHE_NONE</tvar> and <tvar name=code2>$wgCacheDirectory = false</tvar>, otherwise your system message changes may not show up.

If you want your extension to be used on wikis that have a multi-lingual readership, you will need to add localisation support to your extension.

Store messages in <language-key>.json

Store message definitions in a localisation JSON file, one for each language key your extension is translated in.
The messages are saved with a message key and the message itself using standard JSON format.
Each message id should be lowercase and may not contain spaces.
Each key should begin with the lowercased extension name.
An example you can find in the [<tvar name=url>https://github.com/wikimedia/mediawiki-extensions-MobileFrontend/blob/master/i18n/de.json</tvar> MobileFrontend extension].
Here is an example of a minimal JSON file (in this case en.json):

en.json

{
	"myextension-desc": "Adds the MyExtension great functionality.",
	"myextension-action-message": "This is a test message"
}

Store message documentation in qqq.json

The documentation for message keys can be stored in the JSON file for the pseudo language with code qqq.
A documentation of the example above can be:

qqq.json:

{
	"myextension-desc": "The description of MyExtension used in Extension credits.",
	"myextension-action-message": "Adds 'message' after 'action' triggered by user."
}

Load the localisation file

In your extension.json, define the location of your messages files (e.g. in directory i18n/):

{
	"MessagesDirs": {
		"MyExtension": [
			"i18n"
		]
	}
}

Use wfMessage in PHP

In your setup and implementation code, replace each literal use of the message with a call to <tvar name=Message>wfMessage( $msgID, $param1, $param2, ... )</tvar>.
In classes that implement <tvar name=IContextSource></tvar> (as well as some others such as subclasses of SpecialPage), you can use <tvar name=msg>$this->msg( $msgID, $param1, $param2, ... )</tvar> instead.
Example:

wfMessage( 'myextension-addition', '1', '2', '3' )->parse()

Use mw.message in JavaScript

It's possible to use i18n functions in JavaScript too.
Look at <tvar name=1></tvar> for details.

Extension types

Extensions can be categorized based on the programming techniques used to achieve their effect.
Most complex extensions will use more than one of these techniques:

• Subclassing: MediaWiki expects certain kinds of extensions to be implemented as subclasses of a MediaWiki-provided base class:
  • ' – Subclasses of the <tvar name=SpecialPage></tvar> class are used to build pages whose content is dynamically generated using a combination of the current system state, user input parameters, and database queries. Both reports and data entry forms can be generated. They are used for both reporting and administration purposes.
  • ' – Skins change the look and feel of MediaWiki by altering the code that outputs pages by subclassing the MediaWiki class <tvar name=SkinTemplate></tvar>.
• ' – A technique for injecting custom PHP code at key points within MediaWiki processing. They are widely used by MediaWiki's parser, its localization engine, its extension management system, and its page maintenance system.
  • ' – XML style tags that are associated with a php function that outputs HTML code. You do not need to limit yourself to formatting the text inside the tags. You don't even need to display it. Many tag extensions use the text as parameters that guide the generation of HTML that embeds Google objects, data entry forms, RSS feeds, excerpts from selected wiki articles.
• ' – A technique for mapping a variety of wiki text string to a single id that is associated with a function. Both [[<tvar name=1>Special:MyLanguage/Manual:Variable</tvar>|variables]] and [[<tvar name=2>Special:MyLanguage/Manual:Parser functions</tvar>|parser functions]] use this technique. All text mapped to that id will be replaced with the return value of the function. The mapping between the text strings and the id is stored in the array $magicWords. The interpretation of the id is a somewhat complex process – see <tvar name=1></tvar> for more information.
  • ' – Variables are something of a misnomer. They are bits of wikitext that look like templates but have no parameters and have been assigned hard-coded values. Standard wiki markup such as <tvar name=PAGENAME></tvar> or <tvar name=SITENAME></tvar> are examples of variables. They get their name from the source of their value: a php variable or something that could be assigned to a variable, e.g. a string, a number, an expression, or a function return value.
  • ' – {{functionname: argument 1 | argument 2 | argument 3...}}. Similar to tag extensions, parser functions process arguments and returns a value. Unlike tag extensions, the result of parser functions is wikitext.
• ' – you can add custom modules to MediaWiki's [[<tvar name=api>Special:MyLanguage/API:Main page</tvar>|action API]], that can be invoked by JavaScript, bots or third-party clients.
• ' – If you need to store data in formats other than wikitext, JSON, etc. then you can create a new <tvar name=1></tvar>.

Support other core versions

There are two widespread conventions for supporting older versions of MediaWiki core:

• Master: the master branch of the extension is compatible with as many old versions of core as possible. This results in a maintenance burden (backwards-compatibility hacks need to be kept around for a long time, and changes to the extension need to be tested with several versions of MediaWiki), but sites running old MediaWiki versions benefit from functionality recently added to the extension.

• Release branches: release branches of the extension are compatible with matching branches of core, e.g. sites using MediaWiki 1.41 need to use the REL1_41 branch of the extension. (For extensions hosted on [[<tvar name=1>Special:MyLanguage/gerrit</tvar>|gerrit]], these branches are automatically created when new versions of MediaWiki are released.) This results in cleaner code and faster development but users on old core versions do not benefit from bugfixes and new features unless they are [[<tvar name="1">Backporting fixes</tvar>|backported]] manually.

Extension maintainers should declare with the <tvar name=1>compatibility policy</tvar> parameter of the <tvar name=2>{{Extension}}</tvar> template which convention they follow.

License

<translate> <tvar name=1>MediaWiki</tvar> is an open-source project and users are encouraged to make any <tvar name=2></tvar> under an [<tvar name=url>https://opensource.org/licenses/category</tvar> Open Source Initiative (OSI) approved] license compatible with [<tvar name=url2>https://opensource.org/licenses/GPL-2.0</tvar> GPL-2.0-or-later] (Wikimedia's standard software license).

We recommend adopting one of the following compatible licenses for your projects in Gerrit: </translate>

• <translate> GNU General Public License, version 2 or later</translate> (GPL-2.0-or-later)
• <translate> MIT License</translate> (MIT)
• <translate> BSD License</translate> (BSD-3-Clause)
• <translate> Apache License 2.0</translate> (Apache-2.0)

<translate> For extensions that have a compatible license, you can request developer access to the MediaWiki source repositories for extensions.</translate> <translate> To specify the licence in code and with "<tvar name=1>license-name</tvar>" a key should be used to provide it's short name, e.g. "<tvar name=2>GPL-2.0-or-later</tvar>" or "<tvar name=3>MIT</tvar>" adhering to [<tvar name=url>https://spdx.org/licenses/</tvar> the list of identifiers at spdx.org].</translate>

Publishing

To autocategorize and standardize the documentation of your existing extension, please see <tvar name=1></tvar>.
To add your new extension to this Wiki:

<translate> A developer sharing their code in the MediaWiki code repository should expect:</translate>

<translate> Feedback / Criticism / Code reviews</translate>

<translate> Review and comments by other developers on things like [<tvar

Deploying and registering

If you intend to have your extension deployed on Wikimedia sites (including possibly Wikipedia), additional scrutiny is warranted in terms of performance and security.
Consult <tvar name=1></tvar>.

If your extension adds namespaces, you may wish to register its [[<tvar name=1>Special:MyLanguage/Extension default namespaces</tvar>|default namespaces]]; likewise, if it adds database tables or fields, you may want to register those at <tvar name=2></tvar>.

Please be aware that review and deployment of new extensions on Wikimedia sites can be extremely slow, and in some cases has taken more than two years.

Help documentation

You should provide [[<tvar name=1>Special:MyLanguage/Project:PD help</tvar>|public domain help documentation]] for features provided by your extension.
<tvar name=help></tvar> is a good example.
You should give users a link to the documentation via the <tvar name=addHelpLink></tvar> function.

Providing support / collaboration

Extension developers should open an account on Wikimedia's {<tvar name=phab>{ll|Phabricator}}</tvar>, and [[<tvar name=1>Special:MyLanguage/Phabricator/Creating and renaming projects</tvar>|request a new project for the extension]].
This provides a public venue where users can submit issues and suggestions, and you can collaborate with users and other developers to triage bugs and plan features of your extension.

See also

• - provides further developer documentation on how to register extensions and skins.
• – explains how your extension can provide an API to clients
• [[<tvar name=bestp>Best practices for extensions</tvar>|Best practices for extensions]]

Learn by example

• – implements some example features with extensive inline documentation
  • examples git repo with this and other example code
• – a functioning boilerplate extension, useful as a starting point for your own extension (git repo)
  • Read the Example extension, base your own code on the BoilerPlate extension.
• cookiecutter-mediawiki-extension – a cookiecutter template which generates a boilerplate extension (with variables etc.)

• • Allows you to get going quickly with your own extension.

• • Can also generate the BoilerPlate extension.
• - copy specific code from them

References

[[Category:Extension creation{{#translation:}}|Manual:Developing extensions]]