BSPSource is a VMEX-based map decompiler for Source games. It converts BSP files back into VMF ones that can be loaded in Hammer. It also includes numerous bug fixes over VMEX and new features for doing the conversion, such as extracting embedded assets, processing multiple BSPs at once, and more.
Note: Decompiled maps aren't identical to the original VMF files that were used to compile them, and often present issues such as invalid geometry solids or misplaced areaportal brushes.
Note: Some maps protected from decompilation prevent the conversion. However, VMEX "Protection methods" like using No_decomp 1, tools/locked and the obfuscation shape will be ignored. A warning will pop up, but it will decompile anyways.