How to become a MediaWiki hacker

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For other ways to get involved in the MediaWiki community, see How to contributeHow to contribute.

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

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

Overview

MediaWiki is the software that powers Wikipedia, its sister projects and thousands of wikis all over the world. It runs on most operating systems, is written in PHP, primarily uses the MySQL and MariaDB database servers and uses jQuery as the client JavaScript library. Development of MediaWiki is primarily supported by the Wikimedia Foundation, though volunteer community developers play a huge part as well.

This page should help you get started on the path to becoming a contributor to MediaWiki. It is not a tutorial; it just points you to various places where you can go learn whatever is necessary.

Get started

Start by registering for Developer accessDeveloper access and reading the Gerrit tutorial. 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 manual.

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)

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 from GitDownload from Git — Download the latest source code from Git.
• Installation guideManual:Installation guide — 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.

Suggested reading

General recommendations

If you choose to work on a bug report that requires writing or changing code, you might want to at least skim these pages first:

Play media

Watch as a developer fixes a bug, including investigation, git commit, getting it reviewed and merged, and closing the Bugzilla ticket (now replaced by PhabricatorPhabricator).

• The two main paths to get started with MediaWiki development are to fix an annoying little bug in the existing code, or to add a new feature, usually through a MediaWiki extension.
• Coding conventions and any subpages relevant to your task (PHPManual:Coding conventions/PHP, JavaScriptManual:Coding conventions/JavaScript, PythonManual:Coding conventions/Python, …)
• Following the Commit message guidelines, especially the Example section at the bottom, will automatically add a notification about your patch to the corresponding report in PhabricatorPhabricator. Hence there is no need anymore to add a "Please review" comment in the report.
• Check your code against the pre-commit checklist. Don't skip this step; you'll be happy you didn't.
• Getting code reviews. Find and add people as potential reviewers of your patch.
• Amending a change. Don't create a new Gerrit changeset to fix your previous one!
• In most cases when working with MediaWiki, you do not want to hack MediaWiki core unless you really know what you're doing.

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.
• If you have general questions about infrastructure, the software architecture or workflows which are not tied to the specific bug that you want to work on, use generic channels like IRCIRC, mailing lists, or wiki discussion pages. For example, if you have a problem with Gerrit, the Gerrit discussion page could be a good place to ask.
• If you have a specific question about the bug itself, comment in the corresponding PhabricatorPhabricator report. "What do I have to do 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, elaborate what you have tried and found out already, so others can help at the right level. Try to 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.
• Avoid private email or support requests in our social media channels.
• Please 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 drop the question.
• Learn more at CommunicationCommunication.

Communicate that you work on a bug

You do not need to be set as the assignee in a bug report or announce your plans before you start working on a bug, but it would be welcome. At the latest when you are close to creating a patch for the bug, it is good to announce in a comment that you are working on it. Your announcement also helps others to not work on the bug at the same time and duplicate work.

Also note that if a bug report already has a recent link to a patch in Gerrit and has the project "Patch-For-Review" associated, you should choose a different bug to work on instead - avoid duplicating work. If the 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 try to improve it.

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

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

Working on extensions

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

MediaWiki extensions primers

• Developing extensions — How to write an extension for MediaWiki.
• Writing an extension for deployment — If you intend to have your extension deployed on Wikimedia sites (including possibly Wikipedia), additional scrutiny is warranted in terms of performance and security.
• Extension writing tutorial

MediaWiki extensions resources

• List of simple extensions — A simple way to become more familiar with how extensions work.
• 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.
• Special page template — Add a special page to display some handy information.
• Extending wiki markup — Add a parser hook to modify the content of wikitext.

Hands-on suggestions

The following sections describe a few example areas in which you can contribute, but you are not limited to these areas!

In the upper right corner of a task (bug report) in Phabricator you can see the product and component that the problem is located in. This provides you a hint about the Git repository that the code is located in, and about the development team which you could contact if you want to discuss it in a "broader" way (as comments in bug reports should preferably refer to the specific problem described in the report only).

Documentation

• List of open bug reports and enhancement requests related to documentation with the "easy" keyword

Pywikibot

PyWikibot is a Python-based framework to write bots for MediaWiki. Ask your general development questions on the Pywikibot mailing list and the #pywikibot IRC channel.

• List of open easy Pywikibot bug reports and enhancement requests

Multimedia

Ask your general Multimedia development questions on the multimedia mailing list and the #wikimedia-multimedia IRC channel.

• List of open easy Multimedia bug reports and enhancement requests

Mobile Apps

There are numerous applications for mobile devices (Android, iOS, Windows Phone, …) to access Wikimedia wikis. Read the general development information and ask your questions on the Mobile mailing list and the #wikimedia-mobile IRC channel.

• List of open easy Mobile applications bug reports and enhancement requests

Reading

The reading team builds the software that serves our readers. We also manage the mobile web experience. Read the general development information and ask your questions on the Mobile mailing list and the #wikimedia-mobile IRC channel.

• List of open easy reading web tasks

Wikidata

Wikidata is a centralized knowledge base for structured data, such as interwiki references and statistical information. Ask your general development questions on the Wikidata mailing list, the #wikidata IRC channel and on the wiki.

• List of open easy Wikidata bug reports and enhancement requests

Huggle

Huggle is a desktop application for dealing with vandalism on Wikimedia projects, written in C++.

• List of open easy Huggle bug reports and enhancement requests

Browser Tests & Quality Assurance

Automated browser tests help Wikimedia engineers produce quality user facing software faster. See the page on Browser testing for more on what technologies we use and how to get involved. For more general information, see Quality Assurance.

• List of open easy Browser Test bug reports and enhancement requests

Language Engineering (Localization/Translation/Internationalization)

Ask your general Language Engineering development questions on the mediawiki-i18n mailing list and the #mediawiki-i18n IRC channel.

• List of open easy Language Engineering bug reports and enhancement requests

VisualEditor and Parsoid

VisualEditor is MediaWiki's WYSIWYG editor. Ask your general VisualEditor development questions on the wikitech mailing list and the #mediawiki-visualeditor IRC channel.

• List of open easy VisualEditor bug reports and enhancement requests

VisualEditor is powered by Parsoid, a wikitext parser and runtime. Ask your general Parsoid development questions on the wikitext mailing list and the #mediawiki-parsoid IRC channel.

• List of open easy Parsoid bug reports and enhancement requests

Discovery / Search

The Discovery team builds the path of anonymous discovery to a trusted and relevant source of knowledge. Ask your general development questions on the Discovery mailing list and on the #wikimedia-discovery IRC channel.

• List of open easy Discovery / Search bug reports and enhancement requests

Analytics

The Analytics team empowers and supports data-informed decision making in Wikimedia. Ask your general development questions on the Analytics mailing list.

• List of open easy Analytics bug reports and enhancement requests

Design

Fixing design bugs or requests requires existing graphics skills working with a Vector graphics application (e.g. Inkscape). Basic knowledge of CSS can also be helpful for integration. Ask your general development questions on the Design mailing list and the #wikimedia-design IRC channel.

• List of open easy design bug reports and enhancement requests

Skins

Skins allow users to customize the look and feel of MediaWiki. Basic knowledge of CSS and PHP is helpful. Check the project page in Phabricator for more information on each skin and contact information.

• List of open easy skin bug reports and enhancement requests

System messages and localization/translation problems

System messages in MediaWiki or its extensions often need small corrections to the English text, but the source text can only be changed in the code by developers, contrary to translations. This has grown into a large backlog of usually very easy fixes (which might be as easy as fixing a typo).

Also, many messages are unclear and require better documentation (see Localisation#Message documentation). Missing documentation can also be added by just editing the /qqq subpage of the message on translatewiki.net, like all translations, but may require some study of the code to understand what a message is for: it's therefore optimal to start understanding the code, and very useful for the translators (who do not have such skills).

• List of open string change bug reports and enhancement requests (under "Blocked by")

Collaboration

The Collaboration team mainly works on Echo and Flow.

Ask questions regarding Collaboration team projects on the #wikimedia-collaboration IRC channel.

• List of open easy Collaboration team bug reports and enhancement requests

MediaWiki

MediaWiki is the core software which provides basic wiki functionality. It is complex, written in PHP, and some areas might not have clear maintainership. Ask your general development questions on the wikitech mailing list and the #wikimedia-dev and #mediawiki IRC channels.

• List of open easy MediaWiki bug reports and enhancement requests

Phlogiston

Phabricator is used by Wikimedia for project management, software bug reporting and feature requests. Phlogiston is a set of SQL, Python, and R scripts to report on Phabricator data, particularly burnup reports and forecasting.

• List of open easy Phlogiston bug reports and enhancement requests

And many more…

Still not enough ideas? There are more fields you can explore - MediaWiki has hundreds of extensions and tools! Check out the complete list of bugs recommended for new contributors:

• List of open easy bug reports and enhancement requests

If you have any trouble or questions, please ask for help via IRC or feel free to contact Andre Klapper or Quim Gil.

Appendix

MediaWiki contributors at work in Bangalore, India.

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 maintenance/eval.php in MediaWiki provides a basic PHP interpreter with MediaWiki objects and classes loaded.

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.
• How to properly use database transactionsDatabase transactions

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.

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 are constrained to a small region of code.

MediaWiki primers and must-reads

• MediaWiki architecture — A high-level overview of the main components of MediaWiki and how they work with each other.
• Security for developersSecurity for developers — An overview of why and how to write secure code.

MediaWiki resources

• Manual:CodeManual:Code — A list of important files and links to more detailed information.
• Manual:HooksManual:Hooks — 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.
• Manual:Coding conventionsManual:Coding conventions — An overview of general coding conventions within the MediaWiki community.
• Intro-to-MediaWiki workshop syllabusHow to become a MediaWiki hacker/Workshop — Ways to hack MediaWiki, from user preferences to extensions and core.
• Code documentation — Automatically generated documentation from the code and code comments.
• Manual:How to debugManual:How to debug — A guide to debugging MediaWiki.
• Manual:Eval.phpManual:Eval.php — A tool to interact with MediaWiki objects live.

See also

• "Learn how to hack MediaWiki" workshopHow to become a MediaWiki hacker/Workshop
• Developer hubDeveloper hub – When you've thoroughly read the information in this article, it's time to move on to the information in the developer hub.
• MediaWiki Virtual Library (MVL) books; this page forms also part of the MediaWiki Developers Guide.