Checked against official docs on October 16, 2026

AGENTS.md vs CLAUDE.md vs Cursor rules: who reads what

Q: Does Codex read CLAUDE.md?

Not by default. Codex reads AGENTS.override.md or AGENTS.md in each directory. Other filenames are read only if you list them in project_doc_fallback_filenames in ~/.codex/config.toml.

Q: Does Cursor read plain .md files in .cursor/rules?

No. Project rules must use the .mdc extension with frontmatter. Use AGENTS.md if you want plain markdown.

Q: Which file should I use for every agent?

AGENTS.md. Codex, Cursor, Antigravity and most Copilot surfaces read it directly, and Claude Code reads it when there is no CLAUDE.md, or through an @AGENTS.md import.

Short answer: put shared instructions in AGENTS.md. Then add only agent-specific extras: an @AGENTS.md import in CLAUDE.md, .cursor/rules/*.mdc for glob-scoped Cursor rules, and .github/copilot-instructions.md if you need Copilot Chat on GitHub.com.

File	Claude Code	Codex	Cursor	GitHub Copilot	Antigravity
AGENTS.md	Yes (v2.1.277+), by default only when no CLAUDE.md exists	Yes: global ~/.codex/AGENTS.md plus one per directory	Yes, root and nested	Most surfaces (not Copilot Chat on GitHub.com)	Yes, any directory, always on
CLAUDE.md	Yes (primary)	Only if added to project_doc_fallback_filenames	Not documented	Copilot CLI and cloud agent	Not documented
.cursor/rules/*.mdc	/init can import them	No	Yes (.mdc with frontmatter)	No	No
.github/copilot-instructions.md	/init can import it	No	No	Yes	No
GEMINI.md	No	Only via fallback filenames	No	Copilot CLI and cloud agent	Yes
Scoped rules	.claude/rules/*.md (paths)	Nested AGENTS.md / AGENTS.override.md	.cursor/rules (globs)	.github/instructions/*.instructions.md (applyTo)	.agents/rules/*.md (trigger)

Gotchas

Claude Code skips AGENTS.md if you have a CLAUDE.md. Add @AGENTS.md at the top of CLAUDE.md, or set Project instructions to claude-md-and-agents-md in /config. A symlink also works, but it breaks on Windows clones.
Codex reads one file per directory. AGENTS.override.md wins over AGENTS.md in the same folder, and the combined size is capped at 32 KiB by default (project_doc_max_bytes).
Cursor ignores plain .md files in .cursor/rules. Use .mdc with frontmatter, or just use AGENTS.md.
Copilot support differs by surface. Code review on GitHub.com reads AGENTS.md only; the CLI also reads CLAUDE.md and GEMINI.md.
Antigravity rule files need a trigger. AGENTS.md and GEMINI.md need no frontmatter, but every file in .agents/rules/ must declare one.

Convert a rules file between agents →

Frequently asked questions

Does Claude Code read AGENTS.md?

Yes, since v2.1.277, but by default only when there is no CLAUDE.md, .claude/CLAUDE.md or CLAUDE.local.md in your working directory or above it. Put @AGENTS.md at the top of CLAUDE.md to use both.

Does Codex read CLAUDE.md?

Does Cursor read plain .md files in .cursor/rules?

Which file should I use for every agent?

Sources

Claude Code: CLAUDE.md and AGENTS.md · checked 2026-10-16
Codex: custom instructions with AGENTS.md · checked 2026-10-16
Cursor: rules · checked 2026-10-16
GitHub Copilot: custom instructions support · checked 2026-10-16
GitHub Copilot CLI: custom instructions · checked 2026-10-16
Antigravity: rules · checked 2026-10-16