VMX

A proprietary map source format used by the Valve Hammer Editor. It contains information on all brushes and entities in a script format. Identical to a VMF but a backup version of the map. Generated only upon saving it is identical to the map immediately after the last save.

Note: In some cases it may be necessary to roll back to the VMX file, simply delete or rename the VMF and then change the VMX extension to VMF.