How to become a MediaWiki hacker/en

This article is written to help developers learn the basic skills needed to contribute to development of MediaWiki core and MediaWiki extensions.

The main path to get started with Wikimedia development is to contribute to Wikimedia projects that offer mentoring. An alternative without mentoring is to fix a good first bug.

If you are an experienced developer who is familiar with using MediaWiki already, visit the  instead.

For other ways to get involved in the Wikimedia community, see .

Overview
MediaWiki is the software that powers Wikipedia, its sister projects and thousands of wikis all over the world.

Most of MediaWiki and extensions are written in the PHP programming language. JavaScript is used for providing interactive interface elements along with jQuery and Vue.js as client JavaScript libraries.

Some supporting tools are written in other languages, including batch files, shell scripts, makefiles and Python.

MediaWiki is primarily written for the LAMP platform and runs on most operating systems. MediaWiki primarily uses the MySQL or MariaDB database servers.

Development happens in an open source style, is largely coordinated online, and supported by the Wikimedia Foundation, though volunteer community developers play a huge part as well.


 * Development discussion happens on, , and IRC channels. The main developer list is wikitech-l. The main developer IRC channels are and.
 * Source code is stored on and managed using the Git revision control system and can be viewed here
 * Code review is performed on and can be viewed here. Follow this tutorial to set up Git and Gerrit in order to submit patches.
 * Bug reports and feature requests are filed, and projects are coordinated on and can be viewed here

Find or create a task
Before you ever develop a feature or fix a bug in a MediaWiki project, it is important that you do your research about it. This includes:


 * 1) Search Phabricator if an open or closed Task (Document Types field) already exists. If it doesn't, create one. If this is a very small change, don't create one.
 * 2) Find and investigate the code that needs to be changed to implement the feature. Comment your findings on the Phabricator Task if they might be helpful to others who implement it or review your changes.
 * 3) Determine if you can likely add the feature or fix the bug based the code you investigated and the changes needed.  If the task is large or complex, you should find something easier and work your way up to eventually be able to handle tasks of that size. If you believe you can complete it, assign yourself to the Task and begin working on it.

Set up your development environment
Once you have found something you can work on, the next step to developing MediaWiki or an extension is creating an environment to run MediaWiki, its database, and any other external features so that you can develop and test them.

You can install and develop MediaWiki on Linux, Windows, or macOS using any of the three solutions below.

Docker

 * MediaWiki Docker – Run MediaWiki using Docker.

Docker is a good option if you want to setup a MediaWiki installation quickly and are not planning on installing many extensions.

You can also try the new mwcli tool which sets up Docker with a few simple commands and provides basic orchestration functionality between MediaWiki, MySQL, ElasticSearch, Memcached, and other types of containers.

Vagrant

 * MediaWiki Vagrant – Run MediaWiki on a Linux virtual machine using Vagrant.

Vagrant allows you start a MediaWiki instance you can develop as well as allowing you to add and develop any of 250+ extensions - all with a single command.

This saves you installation and configuration time compared to manually adding extensions in a Docker or local installation, but it runs a bit slower than the other two options.

Local installation
MediaWiki can be developed by installing it and its dependencies locally on your system.

It will take much more time to set up than Docker or Vagrant.


 * 1)  — Check hardware requirements and install dependencies
 * 2)  — Download the latest source code from Git.
 * 3)  — Continue with the installation and initial configuration.
 * 4) Set up the various debug modes in your environment to display warning and errors early.

Open a code editor
The two recommended code editors for editing MediaWiki are VSCode and PhpStorm. VSCode is free and PhpStorm is paid, however, you can acquire a PhpStorm license for free if you are a student by linking your GitHub Education account to your JetBrains account, or by requesting a license granted to Wikimedia.

To determine which editor you should install and use, know that all-around, PhpStorm has more and more-powerful features than VSCode. However, PhpStorm takes significantly longer to load on start than VSCode as it builds an index of the entire repository whereas VSCode progressively loads. Therefore, VSCode is typically useful for file-viewing sessions or small changes and PhpStorm for larger changes. It makes sense to have both installed for these reasons.

To develop the MediaWiki codebase that is inside a Docker container you can establish a remote connection to it and open the MediaWiki folder inside it using VSCode or PhpStorm.

Change and test the code
Change the code and view your changes by reloading your MediaWiki browser tab. Make sure to follow. Write and run tests on your code to make sure it works and is formatted properly.

Note, you can save time by ensuring your changes will be accepted before taking the time to write tests. Create a patch without needed tests and ask for someone to review it stating that you will add tests after they review it.

Create a patch
Finally, to submit your code to be reviewed and added to the repository you are contributing to, follow.

PHP
MediaWiki is written in PHP, so you'll need to get familiar with PHP to hack MediaWiki's core.


 * Learn PHP
 * PHP tutorial — Available in many different languages. If you have no knowledge of PHP but know how to program in other object-oriented programming languages, PHP will be easy for you to learn.
 * PHP Programming at Wikibooks.
 * PHP at Wikiversity.


 * PHP resources:
 * The PHP manual — Available in many different languages.
 * PHP coding conventions within the MediaWiki community.


 * Stuff to know:
 * The script  in MediaWiki provides a basic PHP interpreter with MediaWiki objects and classes loaded.
 * Also, the script  in MediaWiki is a replacement of   based on PsySH, see

Database
Many features require some amount of database manipulation, so you'll often need to be familiar with MySQL/MariaDB.


 * Learn MySQL/MariaDB
 * MySQL tutorial — From the MySQL reference manual.
 * MySQL at Wikibooks.


 * MySQL/MariaDB resources
 * MySQL Reference Manuals — Available in many different languages.
 * MariaDB Knowledge Base
 * Database coding conventions within the MediaWiki community.


 * Stuff to know:
 * Test your code with MySQL/MariaDB.
 * MediaWiki currently uses MySQL and MariaDB as the primary database back-end. It also supports other DBMSes, such as PostgreSQL and SQLite. However, almost all developers use MySQL/MariaDB and don't test other DBs, which consequently break on a regular basis. You're therefore advised to use MySQL/MariaDB when testing patches, unless you're specifically trying to improve support for another DB. In the latter case, make sure you're careful not to break MySQL/MariaDB (or write queries that are horribly inefficient in it), since MySQL/MariaDB is what everybody else uses.

JavaScript and CSS
JavaScript and CSS have become omnipresent in front-end code. You don't have to be familiar with JavaScript, jQuery and CSS to work on MediaWiki, but you might need to, depending on what you choose to work on.


 * Learn JavaScript and CSS
 * JavaScript and CSS at Wikibooks.
 * Getting Started with jQuery — A jQuery tutorial.
 * Learning JavaScript — references and sources.


 * JavaScript and CSS resources
 * JavaScript coding conventions within the MediaWiki community.
 * CSS coding conventions within the MediaWiki community.

MediaWiki
The MediaWiki code base is large and some parts are ugly; don't be overwhelmed by it. When you're first starting off, aim to write features or fix bugs which only touch a small region of code.


 * MediaWiki basics and must-reads:
 *  — A high-level overview of the main components of MediaWiki and how they work with each other.
 *  — An overview of why and how to write secure code.


 * MediaWiki resources:
 * — A list of important files and links to more detailed information.
 * — A list of hooks. If you're trying to find what part of the codebase does something, often a good place to start is by searching for the related hooks.
 * — An overview of general coding conventions within the MediaWiki community.


 * Code documentation (class reference) — Automatically generated documentation from the code and code comments.
 * — A guide to debugging MediaWiki.
 * — A tool to interact with MediaWiki objects live.

MediaWiki extensions
If you choose to work on MediaWiki extensions code, the following links provide more information.


 * MediaWiki extensions basics:
 * Developing extensions — How to write an extension for MediaWiki.
 * Extension writing tutorial


 * MediaWiki extensions resources:
 * Best practices for extensions
 * A brief introduction to MediaWiki extension development — A video presentation about how to create a MediaWiki extension (slides).
 * Making a MediaWiki extension — Covers how to develop an extension for MediaWiki, best practices, and how to engage the MediaWiki community. From February 2011.
 * Help for extension developers on the Developer Hub

MediaWiki skins
is helpful if you choose to work on MediaWiki skins.