How to Write an AGENTS.md for Codex, Claude Code, and Cursor

An AGENTS.md file provides essential context for AI coding agents like Codex, Claude Code, and Cursor, ensuring tasks start with consistent commands and boundaries. It should define repository contents, installation, testing, and build processes rather than offering generic advice. To avoid being ignored, instructions must focus on observable rules and specific commands instead of aspirations. In monorepos, placing specialized guidance closer to the relevant code improves reliability and prevents instructions from becoming background noise.