Most engineering teams now have AI agent config files sitting in their repos. CLAUDE.md tells Claude Code how to behave, while AGENTS.md does the same for other agents. .cursorrules, copilot-instructions.md, and a handful of similar files do the same job for other tools. These files live alongside your source code, get reviewed less often than the code itself, and shape what your AI assistants actually do.
Claude Code adds AGENTS.md fallback for repositories shared across coding agents