BMML is a mockup file created with Balsamiq Mockups, an application for designing web-based graphical user interfaced, available for Mac OS and Windows systems. Balsamiq Mockups offers extensive support for XML markup language.

BMML files are only compatible with Balsamiq Mockups version 2. The third iteration of this software uses a new mockup file format designated BMPR, which replaced BMML format. Original version of Balsamiq Mockups stored project data in XML documents.