XCB-Proto provides the XML-XCB protocol descriptions that libxcb uses to generate the majority of its code and API. XCB-Proto is separated from libxcb to allow reuse by other projects, such as additional language bindings, protocol dissectors, or documentation generators.

XCB-Proto also contains language-independent Python libraries that are used to parse an XML description and create objects used by Python code generators in individual language bindings.