Manual:Developing extensions

To use MediaWiki's autoloading mechanism, you add entries to the variable $wgAutoloadClasses. 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 same name as the extension, so your autoloading section might look like this (extension is named MyExtension):

If you need your extension to be compatible with PHP versions earlier than 5.3.0 (as is MediaWiki 1.19 and below), use  instead of.

For complex extensions with multiple classes, your autoloading section might look like this:

Deferring setup
LocalSettings.php runs early in the MediaWiki setup process and a lot of things are not fully configured at that point. This can cause problems for certain setup activities. To work around this problem, MediaWiki gives you a choice of when to run set up actions. You can either run them immediately by inserting the commands in your setup file -or- you can run them later, after MediaWiki has finished configuring its core software.

To defer setup actions, your setup file must contain two bits of code:
 * the definition of a setup function
 * the assignment of that function to the $wgExtensionFunctions array.

The PHP code should look something like this:

Defining additional hooks
See Manual:Hooks.

Adding database tables
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 internationalization
See:
 * or
 * Internationalisation

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 the Extensions FAQ, Developer hub

Internationalization

 * See the main article Internationalisation

(Note: 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 internationalization support to your extension. Fortunately this is relatively easy to do. See also Manual:$wgExtensionCredits for guidelines on the mandatory information.

 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. Assign each message a lowercase message id.

In your setup and implementation code, replace each literal use of the message with a call to. In classes that implement IContextSource (as well as some others such as subclasses of SpecialPage), you can use  instead. Example:  Store the message definition in your internationalization file (MyExtension.i18n.php). This is normally done by setting up an array that maps language and message id to each string. Each message id should be lowercase and they may not contain spaces. A minimal file might look like Manual:Special pages. In your setup routine, load the internationalization file :  

For more information, please see:
 * Localisation – discusses the MediaWiki internationalization 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.
 * Manual:System message
 * Localization checks – discusses common problems with localized messages

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:
 * 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.
 * Variables - 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   or   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 - . Similar to tag extensions, parser functions process arguments and returns a value.  Unlike tag extensions, the result of parser functions is wikitext.
 * Ajax - you can use AJAX in your extension to let your JavaScript code interact with your server side extension code, without the need to reload the page.

Support other core versions
You can visit the extension support portal to keep on top of changes in future versions of mediawiki and also add support for older versions that are still popular.

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

Please also consult Writing an extension for deployment. If your extension adds namespaces, you may wish to register those at namespace registration; likewise, if it adds database tables or fields, you may want to register those at database table and field registration.