jQuery's architecture allows developers to create plug-in code to extend its functionality. Currently there are thousands of jQuery plug-ins available on the web that cover a wide range of functionality such as Ajax helpers, web services, datagrids, dynamic lists, XML and XSLT tools, drag and drop, events, cookie handling, and modal windows.

An important source of jQuery plug-ins is the plugins subdomain of the jQuery Project website. However, in an effort to rid the site of spam, the plugins in this subdomain were accidentally deleted in December 2011. The new site will include a GitHub-hosted repository, which will require developers to resubmit their plugins and to conform to new submission requirements. There are alternative plug-in search engines like jquer.in that take more specialized approaches, such as listing only plug-ins that meet certain criteria (e.g. those that have a public code repository). jQuery provides a "Learning Center" which can help users understand JavaScript and get started developing jQuery plugins.

jQuery plug-ins
Usage styles
Features
Including the library