CLAUDE.md: the project's constitution

the problem it solves

The agent starts every session with an empty memory. What you explained yesterday – "comment in my language", "always run the tests" – you would have to say again today. CLAUDE.md solves this: a file living in the project root that the agent reads automatically at every start. For Codex (and about 20 other tools) the same thing is the AGENTS.md open standard – if you work with both agents, the recommended pattern is: AGENTS.md is the truth, and CLAUDE.md imports it with a single line (@AGENTS.md). That's exactly how it lives on this very site.