MediaWiki is the wiki engine that powers Wikipedia. The project describes itself as “a collaboration and documentation platform” and notes that the software “powers Wikipedia and also this website,” referring to the MediaWiki project’s own site. It is free, open-source software written in PHP, designed to run very large, heavily edited wikis with many contributors and millions of pages.
The software grew out of Wikipedia’s need for a wiki that could scale. Wikipedia launched in early 2001 running a simpler wiki script, but as traffic and content grew it strained under the load. On January 25, 2002, Magnus Manske released a new MySQL-based PHP engine, known at the time as “Phase II,” purpose-built for Wikipedia. When that in turn hit performance limits, Lee Daniel Crocker rewrote it into the “Phase III” software deployed from mid-2002. In 2003 the project adopted the name MediaWiki, a play on the Wikimedia Foundation that had been created to support Wikipedia, and the first numbered release, version 1.1, appeared late that year.
MediaWiki’s lasting contributions are the features that let a wiki grow beyond a small community. Pages are written in wikitext, a plain-text markup that the engine turns into formatted HTML. Templates let editors define reusable fragments, infoboxes, navigation bars, citation formats, that can be inserted into thousands of articles and updated in one place. A category system organizes pages, and namespaces separate articles from discussion, help, and project pages. These mechanisms are what allowed an encyclopedia of millions of articles to maintain a consistent structure.
The engine is also built to be extended. As its documentation puts it, users can “add functionality by installing extensions.” MediaWiki exposes a large set of hooks and a stable extension interface, and a substantial ecosystem of extensions adds capabilities such as visual editing, semantic data, rich media handling, and authentication integrations. This extensibility, combined with strong multilingual support, made MediaWiki attractive far beyond Wikipedia, and it became the standard engine for large institutional and corporate wikis.
Maintained by the Wikimedia Foundation and a broad community of volunteer developers, MediaWiki demonstrated that Ward Cunningham’s original wiki idea could be engineered to run at the scale of one of the most visited websites in the world. Its templates, extensions, and wikitext defined what a production-grade wiki platform looks like.