MediaWiki extensions allow MediaWiki to be made more advanced and useful for various purposes. These extensions vary greatly in complexity. The Wikimedia Foundation operates a Git server where many extensions are hosted, and a directory of them can be found on the MediaWiki website. Some other sites also are known for development of—or support for—extensions are MediaWiki.org, which maintains an extension matrix; and Google Code. MediaWiki code review is itself facilitated through a Gerrit instance. Since version 1.16 MediaWiki also used the jQuery library.