A feature of HTML Kit is the ability to add plugins that extend the program's capabilities. Hundreds of free plugins are available for download via the program's web site (allowing each user to choose only the extra features he or she needs - the default installation of HTML Kit does include some plugins of obvious general utility, such as a library of code snippets and a HTML color picker). Many of the plugins are written by users of the program.
As of 2003, HTML Kit is freeware, although a "professional" version with additional features is in development.