Cursor Rules Guide: .cursorrules and .mdc Best Practices

Master Cursor Rules to customize AI behavior per project. Learn .cursorrules syntax, .mdc format, global vs project rules, rule composition, and real-world examples.

Cursor Rules define custom instructions for AI features, ensuring consistent code generation aligned with your project standards.

Rule Formats

Legacy: .cursorrules

Place in project root. Content is prepended to the system prompt for all AI interactions.

Modern: .mdc Files

Project-specific rules in .cursor/rules/ directory. Each rule is a .mdc file with glob scoping, automatic inclusion, or manual triggering.

Best Practices

1. Keep rules under 500 lines - concise and focused
2. Use concrete names and descriptions for each rule
3. Write specific guidelines: Not "write good code" but "use camelCase, limit functions to 20 lines, include type annotations for all parameters"
4. Update rules as your project evolves to keep AI aligned with current requirements

Global vs Project Rules

• Global: Cursor Settings > General > Rules for AI (applies to all projects)
• Project: .cursor/rules/ directory (project-specific, shareable via Git)

Example Rule Topics

• Code style: naming conventions, formatting standards
• Architecture: component patterns, state management approach
• Testing: test file locations, testing framework usage
• Documentation: JSDoc requirements, README standards
• Security: input validation, authentication patterns

Community Resources

The awesome-cursorrules repository on GitHub contains hundreds of community-contributed rules for React, Next.js, Python, Go, Rust, and many more frameworks.

Sharing Rules

Commit .cursor/rules/ to Git for team consistency. New team members get the same AI behavior immediately.