Extensions

Each extension consists of three parts:

• Setup
• Execution
• Localisation

A minimal extension will consist of three files, one for each part:

MyExtension/extension.json

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

MyExtension/MyExtension_body.php

Stores the execution code for the extension. The file name MyExtension_body.php is conventional but not required. If your extension is complex and involves multiple PHP files, you should follow the convention to put its implementation code in a subdirectory named MyExtension/includes (although the Example and BoilerPlate extensions do not follow this convention). For example, see the SemanticMediaWiki extension.

MyExtension/i18n/*.json

Stores localisation information for the extension.

Originally, extensions were single files, and you may still find some examples of this deprecated style.

When you develop an extension, replace MyExtension above with the name of your extension. Use UpperCamelCase names for its directory and PHP file(s); this is the general file naming convention.[1] (The BoilerPlate extension is a good starting point for your extension. You can also consider using MWStew for generating your extension boilerplate. Also check out the cookiecutter template for MediaWiki extensions on GitHub.)

The three parts of an extension, setup, execution, and localisation, as well as extension types and licensing and publishing your extension are described in the following sections of this page. While developing, you may want to disable caching by setting $wgMainCacheType = CACHE_NONE and $wgCacheDirectory = false, otherwise system messages and other changes may not show up.

Setup

Your goal in writing the setup portion is to consolidate set up so that users installing your extension need do nothing more than include the setup file in their LocalSettings.php file, like this:

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, parser function, special page, custom XML tag, and 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 hooks needed by your extension
• create or check any new database tables required by your extension.
• set up localisation for your extension

Registering features with MediaWiki

MediaWiki lists all the extensions that have been installed on its Special:Version page. For example, you can see all the extensions installed on this wiki at Special:Version. It is good form to make sure that your extension is also listed on this page. To do this, you will need to add an entry to $wgExtensionCredits for each media handler, parser function, special page, custom XML tag, and variable used by your extension. 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+",
	"type": "validextensionclass",
	"manifest_version": 1
}

See Manual:$wgExtensionCredits for full details on what these fields do. 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 extension.json file is written against. As of now the only supported version is 1 (MediaWiki 1.26.x and 1.27.x).

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 the type of your extension. For details, please see the documentation for each type of extension: Gnome-preferences-other.svg Extensions: Development Tag extensions Parser functions Hooks Special pages Skins Magic words API 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 naming conventions (e.g. global variables should begin with $wg).

For example, if your extension is named "Very silly extension that does nothing", you might want to name all your configuration variables to begin $wgVsetdn or $wgVSETDN. It doesn't really matter what you choose so long as 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. Warning Warning: To avoid register_globals vulnerabilities, ALWAYS explicitly set all your extension's configuration variables in extension setup file. Constructs like if ( !isset( $wgMyLeetOption ) ) $wgMyLeetOption = somevalue; do not safeguard against register_globals!

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": "MIT",
	"type": "other",
	"AutoloadClasses": {
		"BoilerPlateHooks": "BoilerPlate.hooks.php",
		"SpecialHelloWorld": "specials/SpecialHelloWorld.php"
	},
	"config": {
		"BoilerPlateEnableFoo": true
	},
	"callback": "BoilerPlateHooks::onExtensionLoad",
	"ExtensionMessagesFiles": {
		"BoilerPlateAlias": "BoilerPlate.i18n.alias.php"
	},
	"Hooks": {
		"NameOfHook": [
			"BoilerPlateHooks::onNameOfHook"
		]
	},
	"MessagesDirs": {
		"BoilerPlate": [
			"i18n"
		]
	},
	"ResourceModules": {
		"ext.boilerPlate.foo": {
			"scripts": [
				"modules/ext.boilerPlate.js",
				"modules/ext.boilerPlate.foo.js"
			],
			"styles": [
				"modules/ext.boilerPlate.foo.css"
			]
		}
	},
	"ResourceFileModulePaths": {
		"localBasePath": "",
		"remoteExtPath": "BoilerPlate"
	},
	"SpecialPages": {
		"HelloWorld": "SpecialHelloWorld"
	},
	"manifest_version": 1
}

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 __autoload($classname) method.

To use MediaWiki's autoloading mechanism, you add entries to the AutoloadClasses 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 MyExtension):

{
	"AutoloadClasses": {
		"MyExtension": "MyExtension_body.php"
	}
}

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

Defining additional hooks

See Manual:Hooks. Adding database tables Warning Warning: If your extension is used on any production WMF-hosted wiki please follow the Schema change guide.

If your extension needs to add its own database tables, use the LoadExtensionSchemaUpdates hook. See the manual page for more information on usage. Set up localisation

See:

• Localisation (summary)
• Localisation (detailed)
• Namespaces

Add logs

On MediaWiki, all actions by users on wiki are tracked for transparency and collaboration. See Manual:Logging to Special:Log for how to do it.

Execution

The technique for writing the implementation portion depends upon the part of MediaWiki system you wish to extend:

• Wiki markup: Extensions that extend wiki markup will typically contain code that defines and implements custom XML tags, parser functions and variables.
• Reporting and administration: Extensions that add reporting and administrative capabilities usually do so by adding special pages. For more information see Manual:Special pages.
• Article automation and integrity: Extensions that improve the integration between MediaWiki and its backing database or check articles for integrity features, will typically add functions to one of the many hooks that affect the process of creating, editing, renaming, and deleting articles. For more information about these hooks and how to attach your code to them, please see Manual:Hooks.
• Look and feel: Extensions that provide a new look and feel to MediaWiki are bundled into skins. For more information about how to write your own skins, see Manual:Skin and Manual:Skinning.
• Security: Extensions that limit their use to certain users should integrate with MediaWiki's own permissions system. To learn more about that system, please see Manual:Preventing access. Some extensions also let MediaWiki make use of external authentication mechanisms. For more information, please see AuthPlugin. In addition, if your extension tries to limit readership of certain articles, please check out the gotchas discussed in Security issues with authorization extensions.

See also Extensions FAQ, Developer hub

Localisation

• Localisation – discusses the MediaWiki localisation engine, in particular, there is a list of features that can be localized and some review of the MediaWiki source code classes involved in localization.
• Creating new messages
• Localization checks – discusses common problems with localized messages

While developing, you may want to disable both cache by setting $wgMainCacheType = CACHE_NONE and $wgCacheDirectory = false, 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. An example you can find e.g. in extension MobileFrontend. 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."
}

Define messages

• Assign each message a unique, lowercase, no space message id; e.g.uploadwizard-desc
• For any text string displayed to the user, define a message.
• MediaWiki supports parameterized messages and that feature should be used when a message is dependent on information generated at runtime. Parameter placeholders are specified with $n, where n represents the index of the placeholder; e.g.

"mwe-upwiz-api-warning-was-deleted": "There was a file by this name, '$1', but it was deleted and you can not reupload the file. If your file is different, try renaming it."

Define message documentation

Each message you define needs to have an associated message documentation entry Message documentation; in qqq.json e.g.

"uploadwizard-desc": "Description of extension. It refers to this event, i.e. the development was paid with this $300,000 grant."

Load the localisation file

In your setup routine, define the location of your messages files (e.g. in directory i18n/): </pre> { "MessagesDirs": { "MyExtension": [ "i18n" ] } } </pre> Use wfMessage in PHP

In your setup and implementation code, replace each literal use of the message with a call to wfMessage( $msgID, $param1, $param2, ... ). In classes that implement IContextSource (as well as some others such as subclasses of SpecialPage), you can use $this->msg( $msgID, $param1, $param2, ... ) 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 Manual:Messages API for details.

Extension types

Gnome-preferences-other.svg Extensions: Development Tag extensions Parser functions Hooks Special pages Skins Magic words API

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:
  • Special pages – Subclasses of the SpecialPage 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 – Skins change the look and feel of MediaWiki by altering the code that outputs pages by subclassing the MediaWiki class SkinTemplate.
• Hooks – 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.
• Tag-function associations – 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.
• Magic words – A technique for mapping a variety of wiki text string to a single id that is associated with a function. Both variables and 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 Manual:Magic words for more information.
  • Variable – 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 Extensions or Blik 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.
  • Parser functions – Template:Functionname: argument 1. Similar to tag extensions, parser functions process arguments and returns a value. Unlike tag extensions, the result of parser functions is wikitext.
• API modules – you can add custom modules to MediaWiki's action API, that can be invoked by JavaScript, bots or third-party clients.

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 1.27 need to use the REL1_27 branch of the extension. (For extensions hosted on 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 backported manually.

Extension maintainers should declare with the compatibility policy parameter of the Template:Extension template which convention they follow.

License

MediaWiki is an open-source project and users are encouraged to make any MediaWiki extensions under an Open Source Initiative (OSI) approved license compatible with GPL-2.0+ (Wikimedia's standard software license).

We recommend adopting one of the following compatible licenses for your projects in Gerrit:

• GNU General Public License, version 2 (GPL-2.0+)
• MIT License (MIT)
• BSD License (BSD-3-Clause)
• Apache License 2.0 (Apache-2.0)

For extensions that have a compatible license, you can request developer access to the MediaWiki source repositories for extensions. To specify the licence in code and with "license-name" a key should be used to provide it's short name, e.g. "GPL-2.0+" or "MIT" adhering to the list of identifiers at spdx.org.

Publishing

To autocategorize and standardize the documentation of your existing extension, please see Template:Extension. To add your new extension to this Wiki:

A developer sharing their code on the MediaWiki wiki or code repository should expect:

Feedback / Criticism / Code reviews

Review and comments by other developers on things like framework use, security, efficiency and usability.

Developer tweaking

Other developers modifying your submission to improve or clean-up your code to meet new framework classes and methods, coding conventions and translations.

Improved access for wiki sysadmins

If you do decide to put your code on the wiki, another developer may decide to move it to the MediaWiki code repository for easier maintenance. You may then request commit access to continue maintaining it.

Future versions by other developers

• New branches of your code being created by other developers as new versions of MediaWiki are released.
• Merger of your code into other extensions with duplicate or similar purposes — incorporating the best features from each extension.

Credit

• Credit for your work being preserved in future versions — including any merged extensions.

• • Similarly, you should credit the developers of any extensions whose code you borrow from — especially when performing a merger.

Any developer who is uncomfortable with any of these actions occurring should not host their code directly on the MediaWiki wiki or code repository. You are still encouraged to create a summary page for your extension on the wiki to let people know about the extension, and where to download it. You may also add the Template:Extension exception template to your extension requesting other developers refrain from modifying your code, although no guarantees can be made that an update will be made if deemed important for security or compatibility reasons. You may use the current issues noticeboard if you feel another developer has violated the spirit of these expectations in editing your extension.

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 Review queue.

If your extension adds namespaces, you may wish to register its default namespaces; likewise, if it adds database tables or fields, you may want to register those at database table and field registration.

Help documentation

You should provide public-domain help documentation for features provided by your extension. Help:CirrusSearch is a good example. You should give users a link to the documentation via the addHelpLink() function.

Providing support / collaboration

Extension developers should open an account on Wikimedia's Phabricator, and 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

• Extension:Example – implements some example features with extensive inline documentation
  • examples git repo with this and other example code
• Extension:BoilerPlate – 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 template for the python tool cookiecutter to generate a boilerplate extension (with variables etc.)
  • Allow you to get going quickly with your own extension. Can also generate the BoilerPlate extension.
• List of simple extensions - copy specific code from them
• API:Extensions – explains how your extension can provide an API to clients
• Extending wiki markup
• Project:WikiProject Extensions
• Coding conventions
• Best practices for extensions
• ResourceLoader