.cursorrules is a file in your project root that gives Cursor persistent instructions about your codebase, conventions, and preferences — applied to every AI interaction.

What to Put in .cursorrules

# Project: E-commerce API
# Stack: Node.js, TypeScript, PostgreSQL, Express

- Always use async/await, never callbacks
- Use Zod for all input validation
- Follow the repository pattern for database access
- All API responses must use the ApiResponse wrapper type
- Write tests with Jest, aim for 80%+ coverage
- Use conventional commits format
- Never use 'any' TypeScript type

Why It Matters

Without .cursorrules, every Composer or Chat response may use different patterns. With it, all AI output follows your exact standards.

Reference:

Rules for AI documentation

https://docs.cursor.com/context/rules-for-ai