If you are an experienced developer who is familiar with using MediaWiki already, visit the Developer hub instead.
For other ways to get involved in the Wikimedia community, see How to contribute.
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.
MediaWiki is primarily written for the LAMP platform[1] and runs on most operating systems.
MediaWiki primarily uses the MySQLorMariaDB database servers.[2]
Development happens in an open source style,[3] is largely coordinated online, and supported by the Wikimedia Foundation, though volunteer community developers play a huge part as well.
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:
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.
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.
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 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 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 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.
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 VSCodeorPhpStorm.
Change and test the code
Change the code and view your changes by reloading your MediaWiki browser tab. Make sure to follow Manual:Coding conventions.
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 Gerrit/Tutorial.
Communication tips and guidelines
A developer fixes a bug in a MediaWiki extension, including investigation, git commit, getting it reviewed and merged, and closing the Bugzilla ticket (now replaced by Phabricator).
Follow these tips to communicate effectively and get help from community members.
No need to ask for permission: You can work on unassigned tasks without asking someone to assign them to you. There is no authority who assigns tasks or who needs to be asked first.
If a task already has a recent patch in Gerrit, choose a different task to work on instead.
If an existing patch in Gerrit has not been merged and has not seen any changes for a long time, you could improve that existing patch, based on the feedback in Gerrit and in the task.
Do your research: When you consider working on a task, do research before you start coding. Look at the code, try to understand what it is supposed to do, read related documentation, and try to find the places where you need to make code changes.
In a Phabricator task, use the project tags in the side bar to find the code repository for the task.
If you have no idea at all how to fix the bug, consider finding an easier one first.
You do not need to announce your plans before you start working on a task, but you should communicate that you are working on the task.
When you start work, set yourself as task assignee by clicking Edit Task… in Phabricator, and set your Phabricator username in the Assigned To field. This communicates to others that you are working on it, so they don't duplicate work.
When your plans or interests change: If you are no longer working on a task, remove yourself as the assignee of the task. This tells others that they can work on the task, and they won't expect you to still work on it.
In Phabricator tasks, discuss only specific questions about the topic of that task. Don't use Phabricator to ask general questions, like how to set up a development environment or how to fix problems with Gerrit.
Be specific and provide context: Instead of simply asking "Can you give me more info?", "Please guide me", or "Please tell me how to start", include the following information in your question:
What are you trying to achieve?
What have you already tried? Copy and paste your commands and their output (if not too long) instead of paraphrasing in your own words.
What have you found out already during your research? Include links to code, documentation, or other resources you already consulted.
Use specific titles and subject lines in your communication. "Proposal draft" or "Need help" is not specific.
Keep conversations readable: When you reply in Zulip, in Phabricator tasks, or on mailing lists, only quote sections of previous comments that are relevant to your response. If you quote a complete previous comment, it makes threads hard to read.
Use Inclusive language: Instead of using terms that assume a gender identity (like "guys", "madam", or "sir") use the name of the person instead.
Ask in the right place
Ask in public: Do not send private messages if your conversation topic is not secret. Private messages don't help others.
Ask and discuss in the best place:
In Phabricator tasks, discuss only specific questions about the topic of that task.
Ask general technical questions, like how to set up a development environment or how to fix problems with Gerrit, in the places listed on Communication.
If you take part in an outreach program, then Zulip is for discussing questions about the outreach programs themselves.
Be patient
After you post your question:
Do not ask people for code review in a separate message. People receive Gerrit and Phabricator notifications and will respond when they can.
When seeking input and comments, especially during weekends and holidays, you may need to wait until business hours resume. On chat channels like IRC: if nobody answers, try again at a different time; don't just give up!
If you don't get an answer even after waiting and being patient, consider if other Communication channels might be a better place to ask your question.
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.
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.
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
MediaWiki architecture — A high-level overview of the main components of MediaWiki and how they work with each other.
Manual:Code — A list of important files and links to more detailed information.
Manual: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 conventions — An overview of general coding conventions within the MediaWiki community.
Making a MediaWiki extension — Covers how to develop an extension for MediaWiki, best practices, and how to engage the MediaWiki community. From February 2011.
↑MediaWiki runs on most platforms that can support PHP, however, the lack of certain utilities or operating system features may limit the functionality or performance of MediaWiki on non-LAMP platforms.
↑MediaWiki has support for DBMS other than MySQL and MariaDB, including PostgreSQL, SQLite
↑Developers are a mix of volunteers and paid staff (or contractors) for various organizations. For a full list of who works on the MediaWiki code, read the Developers article.
