AGENTS.md in plain English: one file of house rules for every coding agent

Tired of typing “plan first, keep it small, run the tests” into every new chat? AGENTS.md is one plain-text file of house rules in your project that coding agents read on their own, so you write the rules once and stop repeating yourself. Codex reads it before doing any work, and Claude Code reads it too when there is no CLAUDE.md in the way.

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