The BLF file format is a forma that is being used for Blam engine's user content files, and other external files such as map info and some DLC.

The BLF format uses a simplified version of the regular tag system Bungie uses for its .map files. A tag is defined using 4 ASCII bytes followed by an int32 which defines the total size of the tag.

The BLF header is composed of a _blf tag which stores the description of the BLF file its self, sometimes in several languages if the file is native to the retail Disc. All BLF files use the Big endian byte order.

The BLF footer is compsoed of a _eof tag which signifies the memory reader to stop reading the contents of the file. Zero padding may occur after the eof as well.


  • The user content BLF files in Halo: Reach include a ssig tag before the _eof. It may be Bungie's newest counteraction to Halo 3's user content exploits.
  • Screenshot BLF files in Halo: Reach now contain several other tags which provide player information and other unmapped tag systems which can only be speculated as being counteracts to any exploits the user may do.
  • User content BLF files typically have a chdr tag which defines the name, author, description, created and last modified dates, and the name of the last person who modified it.