Jointed Model Skeleton (JMS) is text-based geometry file format used when importing levels and models into Halo's tag formats. The file contains information such as vertices, normals, material names, UV coordinates, and rigging.

JMS serves as a common target from 3D editors. You can export JMS directly from Blender and 3ds Max using their respective community-made addons, or by first exporting to FBX and using Tool to convert to JMS.

Using Tool, a JMS file is then compiled into one of Halo's geometry tags. For example with H1:

Starting with H2, the ASS format was introduced to replace JMS for level geometry specifically (though JMS is technically still supported). With Reach, Granny (GR2) is the new unified format instead.