Set up Cursor Rules for your project

Cursor without rules is a capable assistant that doesn't know your project. Cursor with well-written rules is an assistant that already knows your stack, conventions, and constraints before you type a word. The setup takes fifteen minutes. The payoff is every session that follows.

What we tried

We started by dumping everything about our project into a single rules file. Stack details, naming conventions, architectural decisions, testing patterns, preferred libraries. It was thorough. It was also too long — Cursor was technically aware of everything, but the rules were so dense they seemed to dilute each other.

What happened

We split the rules by concern: one rule for stack and conventions, one for testing, one for commit standards. Shorter, more focused rules applied more reliably than one long one.

What we learned

The new rules format (.cursor/rules/):

Cursor moved from a single .cursorrules file to a directory of .mdc files. The new format is more powerful — rules can be scoped to specific file patterns and toggled on per-session.

your-project/
└── .cursor/
    └── rules/
        ├── project.mdc       ← always-on project context
        ├── testing.mdc       ← applies to *.test.ts files
        └── commits.mdc       ← applies when writing commit messages

MDC file structure:

---
description: Project stack and conventions
globs: []
alwaysApply: true
---

# Stack

Next.js 15 App Router, TypeScript strict, Tailwind CSS v4.
Path alias: @/* → src/*.

# Conventions

- Functional components only
- `cn()` from src/lib/utils.ts for conditional class names
- No inline styles
- No `any` without a comment

Key frontmatter fields:

• alwaysApply: true — rule loads in every chat and Composer session
• globs — array of file patterns that trigger this rule (e.g. ["**/*.test.ts"])
• description — shown in the rules picker; be specific

Start with one rule:

Don't create five rules on day one. Create one — the stack and conventions rule, set alwaysApply: true. Use it for a week. Add rules only when you catch Cursor making the same mistake twice. That mistake is telling you what rule to write next.

Verify it's loading:

In any Cursor chat, type @rules to see which rules are active for the current file and session. If your rule isn't listed, check the frontmatter syntax — a YAML error silently prevents loading.

Next

• Next cable — Migrating from .cursorrules to the new rules format.
• Next cable — Team Cursor rules: sharing conventions across a multi-developer project.