AGENTS.md is a filename convention for agent instructions: one markdown file at the repository root that AI coding agents read before acting. Codex CLI, GitHub Copilot, Cursor, Windsurf, Amp, and Devin all read it; Claude Code still reads CLAUDE.md and Gemini CLI reads GEMINI.md.
The convention ended the format argument — most tools now agree on where instructions live. It did not end the copy problem: every repository, clone, and worktree still carries its own AGENTS.md, and the copies still diverge.
One laptop held 111 AGENTS.md files with 19 distinct contents. The format was never the expensive part; the copies are.
This entry is part of the untactit glossary. Definitions draw on measured write-ups published on the blog.
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