The Unofficial Doom Specs is the title of a text document by Matt Fell which gives details for many of the technical aspects of Doom. Most usefully, the specs give detailed information about the structure of WAD files and the various different types of resources they contain.
The specs cover:
- The format of graphics
- Texturing lumps (TEXTURE1, TEXTURE2 and PNAMES)
- The basic level format: Linedefs, Sidedefs, Sectors, Blockmap, Vertices and Things.
- The format of lumps generated by the BSP builder: NODES, SEGS, SSECTORS; how the BSP tree is used in rendering is not explained.
Documentation on several pieces of data are conspicuously absent from the file:
- Detail on the .MUS format used for Doom's music, other than the header
- The format of PC speaker sound effects
The specs also give other technical information. Included is data about changes to the Doom IWAD file made between versions. The file format of demo files is described. Information about strings inside the Doom executable file is also included; this perhaps served as a base for the development of DeHackEd.
The file has not been officially updated since 1994. It is likely for this reason that several pieces of information are absent, and some of the information is speculative or even incorrect in light of the source code release.