Rules file
A standing instruction file kept in a project (often named CLAUDE.md, AGENTS.md, or similar) that a coding agent reads at the start of every session: conventions, commands, things never to do.
“Put 'never run migrations on prod' in the rules file.”
See also
Part of the Extended list
Rules file is on the Extended list: builder jargon, industry terms, and newer slang for when you want to go further. It entered common use around 2025.