MediaWiki is a free and open-source wiki engine. It was developed for use on Wikipedia in 2002, and given the name "MediaWiki" in 2003. It remains in use on Wikipedia and almost all other Wikimedia websites, including Wiktionary, Wikimedia Commons and Wikidata; these sites continue to define a large part of the requirement set for MediaWiki. MediaWiki was originally developed by Magnus Manske and improved by Lee Daniel Crocker. Its development has since then been coordinated by the Wikimedia Foundation.
MediaWiki is written in the PHP programming language and stores all text content into a database. The software is optimized to efficiently handle large projects, which can have terabytes of content and hundreds of thousands of hits per second. Because Wikipedia is one of the world's largest websites, achieving scalability through multiple layers of caching and database replication has been a major concern for developers. Another major aspect of MediaWiki is its internationalization; its interface is available in more than 300 languages. The software has more than 1,000 configuration settings and more than 1,800 extensions available for enabling various features to be added or changed.
Besides its use on Wikimedia sites, MediaWiki has been used as a knowledge management and content management system on many thousands of websites, public and private, including the websites Fandom and wikiHow, and major internal installations like Intellipedia and Diplopedia.
MediaWiki is free and open-source software and is distributed under the terms of the GNU General Public License version 2 or any later version. Its documentation, located at www.mediawiki.org, is released under the Creative Commons BY-SA 3.0 license and partly in the public domain. Specifically, the manuals and other content at MediaWiki.org are Creative Commons-licensed, while the set of help pages intended to be freely copied into fresh wiki installations and/or distributed with MediaWiki software is public domain. This was done to eliminate legal issues arising from the help pages being imported into wikis with licenses that are incompatible with the Creative Commons license. MediaWiki development has generally favored the use of open-source media formats.