The XCB util module provides a number of libraries which sit on top of libxcb, the core X protocol library, and some of the extension libraries. These experimental libraries provide convenience functions and interfaces which make the raw X protocol more usable. Some of the libraries also provide client-side code which is not strictly part of the X protocol but which has traditionally been provided by Xlib.

The XCB util-errors module provides a utility library that gives human readable names to error codes, event codes, and also to major and minor numbers.