UML file extension is commonly related to files used in IT systems development. UML (Unified Modeling Language) format is used for describing objects, for example computer program objects, or other hierarchical data structures.

UML files use XLM data format. The files structure can be visualized as a/in form of a diagram hierarchical structure. IDE tools allow users to directly modify the diagrams and save them as UML files. UML files can also be used to automatically generate source code as opposed to having to manually write it.