When you say “I’m going to reverse-engineer a binary file format,” people picture C, or Python with struct , or Kaitai. Nobody pictures Ruby. Ruby is for web apps and DSLs and being pleasant; it is not, in the popular imagination, for byte-banging floats out of a 2003 racing game. That popular imagination is wrong. The reader for Codemasters’ BIGF archive format — the container that holds the AI data in TOCA Race Driver — is pure, dependency-free Ruby, and it reads four different games’ archives. I should be upfront about how it came to be: this was reverse engineering done with an AI the whole way — me steering, deciding what to trust and verifying every claim against the bytes; the model drafting code, recalling the corners of the standard library, and proposing hypotheses I then tested. What follows is the part of Ruby that made that collaboration genuinely pleasant: Ruby strings are byte buffers, and String#unpack is a tiny, fast binary parser hiding in plain sight.…