CLAUDE.md and AGENTS.md in the same project - how to avoid maintaining two files

I spent two weeks with a CLAUDE.md and an AGENTS.md saying different things about the same repository.

I found out the worst way: an agent did exactly what the rule forbade, and the rule was there. In the other file.

(abertura sugerida: confira se bate com a sua memória e ajuste para a sua voz antes de postar)

Claude Code reads CLAUDE.md. Codex reads AGENTS.md. Use both in one project and you have two files describing how to work in your code, with nothing forcing them to say the same thing.

Why two drifting files cost you