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. Note that in most cases when working with MediaWiki, you do not want to hack MediaWiki core unless you really know what you're doing.

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.

MediaWiki is written in the PHP programming language. It uses jQuery as the client JavaScript library.

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 various mailing lists and IRC channels. The main developer list is wikitech-l. The main developer IRC channels are #mediawiki and #wikimedia-dev.
 * Source code is managed using the Git revision control system.
 * Code review is performed on . Follow this tutorial to set up Git and Gerrit in order to submit patches.
 * Bug reports and tasks are managed on Phabricator.

This page should help you become a contributor to MediaWiki. It is not a tutorial; it just points you to various places where you can go learn whatever is necessary.

Set up your development environment
Most projects use Git and Gerrit. Follow the Gerrit tutorial to set up your developer account. Then you can move on to downloading our code, making changes, testing them, and submitting patches. There are two ways to set up your development environment: using a pre-configured virtual machine setup (Vagrant or Docker), or a manual configuration approach.

Virtual Machine with Vagrant

 * Vagrant installation — These steps will install MediaWiki server with all the requirements inside a Linux virtual machine (can be used on Linux, Windows, or Mac hosts).

Docker development environment

 * MediaWiki Docker – Run MediaWiki using Docker (can be used on Linux, Windows or macOS hosts).

Manual installation

 * Installation requirements — Check hardware requirements, and install a LAMP, MAMP or WAMP server (Linux, Mac or Windows, plus Apache, MySQL/MariaDB and PHP).


 * — Download the latest source code from Git.
 * — Continue with the installation and initial configuration.
 * Set up the various debug modes in your environment to display warning and errors early.

It's not necessary to download Wikipedia database dumps in order to develop MediaWiki features. In fact, in many cases it's easier to use a near-empty database with a few specially-crafted test pages. However, if for some reason you want to have a copy of Wikipedia, you can get a dump.

Communication tips and guidelines


Feedback, questions and support

 * You are expected to do some basic research yourself first: Look at the code, try to get some understanding what it is supposed to do, read related documentation, try to find the probable place(s) where you need to make changes in order to fix the bug.
 * In a Phabricator task, see the project tags in the side bar to find out which code repository a task is about.
 * If you have general questions which are not tied to the specific task that you want to work on, use generic channels like IRC chat or mailing lists but not the specific task. Questions how to set up your development environment or how to use Gerrit are out of scope for a task.
 * If you have a specific question about the bug itself, comment in the corresponding bug report (normally a task in ). "Can you give me more info how to fix this bug?" is not a good question to start with: The more specific your questions are, the more likely somebody can answer them quickly. If you have no idea at all how to fix the bug, maybe that bug is not (yet) for you – please consider finding an easier one first.
 * When asking, explain what you have tried and found out already, so others can help at the right level. Be specific – for example, copy and paste your commands and their output (if not too long) instead of paraphrasing in your own words. This avoids misunderstandings.
 * Do not ask if you can work on a task. Do not ask to assign a task to you.
 * Avoid private email or support requests in our social media channels.
 * Be patient when seeking input and comments. On IRC, don't ask to ask, just ask: most questions can be answered by other community members too if you ask on an IRC channel. If nobody answers, please ask on the bug report or wiki page related to the problem; don't just give up.

Communicate that you work on a task
Do not ask if you can work on a task. Do not ask to assign a task to you. You do not need to announce your plans before you start working on a bug, but it would be welcome. You are welcome to set yourself as the assignee in a task: Use the dropdown Add Action… → Assign/Claim in Phabricator. At the latest when you are close to proposing a patch for the task, it is good to announce in a comment that you are working on it. Your announcement helps others to not work on the bug at the same time and to not duplicate work.

Also note that if a task already has a recent link to a patch in Gerrit and has the project "Patch-For-Review" associated in Phabricator, choose a different task to work on instead – avoid duplicating work. If an existing patch in Gerrit has not been merged and has not seen any changes for a long time, you could also pick up that existing patch and improve it, based on the feedback in Gerrit and in the task.

If you stop working on a task, remove yourself as the assignee of the task, so others know that they can work on the task and don't expect you to still work on it.

By communicating early you will get more attention, feedback and help from community members. 

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 topic 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 Manual:Shell.php.

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 5.0 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