It is written in the C programming language and in normal operation uses a text-mode user interface. Irssi was written primarily to run on Unix-like operating systems but also runs under Microsoft Windows, using Cygwin. Irssi can also be compiled and run under Windows natively, but doing so adds additional work to access many of its useful features. Several versions are available for the UNIX-based Mac OS X, including a text-mode version using Fink or MacPorts, a native graphical version named MacIrssi, another graphical version called IrssiX, and formerly the Cocoa client Colloquy (which now uses its own IRC core implementation). Unlike some text mode IRC clients, Irssi is not based on the ircII code, and was written from scratch. This freed the developers from having to deal with the constraints of an existing codebase, allowing them to maintain tighter control over issues such as security and customization. Numerous modules and Perl scripts have been made available for Irssi to customise how it looks and operates. Irssi may be configured by using its user interface or by manually editing its configur