I used to think AI coding assistants plateaued because the models weren't good enough. Then I watched a teammate's Cursor produce cleaner code than mine on the same task, with the same model. The difference was his .cursor/rules/ folder. His assistant had a contract; mine was improvising.
A good Cursor rule isn't a motivational poster ("write clean code"). It's a specific, enforceable check scoped to when it matters. Below are ten rules I've stolen, refined, and now copy into every repo. Steal the ones that fit your stack. Each is a real .mdc file you can paste into .cursor/rules/.
Quick refresher on .mdc frontmatter
Cursor's Project Rules live in .cursor/rules/*.mdc. Three frontmatter fields decide when a rule loads:
alwaysApply: true — in context on every request. Keep these short and universal.
