Word
Rules file
A rules file is a file at the top of your project that tells your agent how to behave in this project.
Also called: CLAUDE.md, project instructions
It says what this project is, what your agent must never touch, which things it may run without asking, and how you want work explained back to you. By convention it's named CLAUDE.md, a markdown file.
You'll meet it early, because an agent without one re-learns your preferences every session and forgets them again by morning.
What people get wrong is writing wishes. Write rules an agent can obey and you can check: named files, named limits, a named point where it stops and asks.