SITX is a file format that is a compressed data archive. Such files are most often associated with StuffIt version 7.0 and later. It is a very efficient format whose files can be up to 98% smaller than the original data before being compressed. This is important for large collections, saves space on data carriers and facilitates the distribution of large amounts of data, e.g. using the Internet.

This compression format supports 512-bit data encryption and preserves file attributes, including file permissions.