# How to write rules for AI agents that every agent on the project reads

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Canonical page: https://hatchedstacks.com/library/how-to-write-rules-for-ai-agents
Last checked: 2026-10-20

To write rules for AI agents, put them in one plain file at the root of your project, usually AGENTS.md, keep each rule short and specific, and back the rules that must never be broken with a check that runs before the agent acts.

Where your rules should live depends on how many agents read them.

| If you are | Start with |
| --- | --- |
| Using one coding agent | One AGENTS.md at the root of the project. Claude Code reads it in place of its own CLAUDE.md, and Cursor reads it alongside its own rules |
| Using several agents on the same project | AGENTS.md, which tools such as Codex, Cursor, Gemini CLI and GitHub Copilot's coding agent read, so one file serves them all |
| Running agents where one mistake costs money | Rules for guidance, plus a hook that blocks the risky command before it runs |

## What a good rule looks like

A good rule names the thing and says what to do with it. "Be careful with customer data" gives the agent nothing to act on. "Never paste a customer's email address into a chat; use their customer ID" does.

Write each rule as one line, put the reason after it, and delete any rule the agent has never needed.

## Where the file goes

- AGENTS.md sits at the root of the repository. In a large project each subfolder can have its own, and the nearest one wins.
- Claude Code reads CLAUDE.md files at project, user and organisation level, can read AGENTS.md instead, and scopes rules to file types in a .claude/rules folder.
- Cursor keeps its own project rules in a .cursor/rules folder and also reads AGENTS.md.

## Rules guide the agent; hooks enforce them

A rules file is something the agent reads, so it can still get a rule wrong on a bad day. Claude Code's own documentation says it treats these files as context, not enforced configuration, and points you to a hook when an action must be blocked whatever the agent decides.

So split your rules in two. Most stay as guidance in the file. The handful that would cost you money, data or a client get a hook: a small check that runs before the command and stops it.

## Questions

**AGENTS.md or CLAUDE.md: which one to use?**

If more than one agent works on the project, AGENTS.md, because most coding agents read it and Claude Code can read it too.

**Should rules and memory share one file?**

Keep them apart. Rules say what to do; memory says what is true. Mixed together, the file grows until the rules get lost in it.

## Sources

- [AGENTS.md](https://agents.md/), checked 2026-10-20
- [Claude Code: How Claude remembers your project](https://code.claude.com/docs/en/memory), checked 2026-10-20
- [Cursor: Rules](https://cursor.com/docs/rules), checked 2026-10-20