Claude Code Rules Files: where rules should actually live.

Ryan “RyMac” McKinney · USMC · 22 August 2026 · 3 minute read

A rule your AI ignores is worse than no rule, because you stop checking. Most people fix that by making a rules folder. I did too. It did not work, and the reason it did not work is the useful part.

Why the rules folder is tempting

You have rules. They pile up. Putting them in their own folder feels like organising, and organising feels like progress. Everything about it looks correct, which is exactly the trap in CLAUDE.md best practices.

Then the rules get ignored anyway, and now they are ignored somewhere tidier.

The actual reason rules get ignored

Not the location. The rule was never checkable.

Not a rule: write in a friendly tone. Keep it professional. Be concise.

A rule: never use an em dash. Numbers are always digits, never spelled out. One path, never a list of options.

You can look at the output and know instantly whether the second kind was followed. The first kind gets a shrug from a machine and from a person, and you find out it was ignored at the worst moment. Every rule in my own file passes that test, because the ones that did not are gone.

Where a rule belongs

True everywhere, about you? The file in your home folder. How you like to be talked to, what you cannot read, what you never want to see again.

True for this project only? That project's file. This client's tone, this brand's forbidden words, this repo's conventions.

True only today? Not a rule. That is the desk file, and confusing the two is a large part of why things get lost.

The 3 places all get read, and Anthropic’s own documentation is the right reference for exactly where each one sits.

When a folder does earn its place

One case: the rule is long, and it is only needed sometimes.

A 400 line style guide should not be re-read at the start of every session for a job that has nothing to do with writing. Put it in a file, and have the map say when to go get it. That is a pointer, not a filing cabinet, and it keeps the cost off the sessions that do not need it, which is the same reasoning as everything else on the desk.

What does not earn its place is 30 one-line rules in 30 files. That is a folder of sticky notes.

The rule that fixed the most for me

Mine says: I cannot write code. Explain it like I am in 9th grade.

One line. It changed every answer I have received since. It is checkable, because I can tell in a sentence whether I understood it, and it is the entire reason this works for somebody who is not a developer.

Write 3 rules tonight

1. Think of the last time you had to correct the same thing twice.

2. Write it as something a stranger could check by looking.

3. Put it in the file that is read first, not in a new folder.

4. Add the reason next to it, 1 line, so you do not delete it in 3 months when it looks arbitrary.

5. Stop at 3. Rules earned by something going wrong stick. Rules invented on day 1 because they sound wise get ignored.

Where that file sits, and what sits under it, is the Claude directory structure.