AGENTS.md is a plain Markdown file in a code project that tells AI coding agents how to work on it: setup commands, tests and code style.
In plain words
A README is written for people. AGENTS.md is a separate file written for AI coding agents, a predictable place for the extra detail they need, such as how to build the project, how to run tests and which conventions to follow. It is an open format, and coding agents such as OpenAI's Codex read it automatically before starting work.
A quick example
A typical AGENTS.md has a short Setup section (install dependencies, start the dev server, run the tests) and a Code style section (for example, use strict TypeScript and single quotes). An agent reads it first, so it runs the right commands without being told each time.
Where you'll meet it
- Open-source repositories used with AI coding agents.
- Team projects that want consistent agent behaviour.
Related
Sources
- DocsAGENTS.md, agents.md · read 29 Sept 2026
- DocsCustom instructions with AGENTS.md, OpenAI Codex documentation · read 29 Sept 2026
Checked by WhatIsAI against the sources above · 29 Sept 2026. Spotted an error? Report it.