Cursor Rules: Complete Guide to Customizing Your AI IDE

Cursor Rules are instructions stored in .cursorrules or Settings that customize how Cursor's AI behaves in your projects -- enforcing coding style, testing conventions, framework patterns, and constraints. They apply to Composer, Agent mode, and chat across all models. This guide explains how to write and use them effectively.

TL;DR

• Place rules in .cursorrules at your project root for project-specific behavior, or in Settings > Rules for AI for global defaults.
• Rules should specify concrete conventions: style, testing framework, tech stack, forbidden patterns, and file references.
• Project rules take precedence over global rules when both exist.
• Be specific ("Use 2-space indent. Prefer named exports.") rather than vague ("Write good code.").
• Keep rules concise and updated as your project evolves; stale rules that contradict actual code produce worse output.

Quick Answer

Cursor Rules = instructions that tell Cursor how to code for your project. Put them in .cursorrules (project root) or Settings > Rules for AI (global). Use them for style, conventions, and constraints. Cursor

Where Rules Live

Project rules take precedence when both exist.

What to Put in Rules

Example .cursorrules

# Project: MyApp

- Next.js 15, TypeScript, Tailwind
- Use server components by default; add "use client" only when needed
- Write tests in Vitest; colocate with src
- No console.log in production code
- Follow our existing API patterns in /lib/api

Best Practices

Rules vs Other Context

• Rules: Persistent instructions; always in context.
• @-mentions: One-off context (files, docs, web).
• Chat history: Conversational context.

Rules set the baseline; @-mentions add task-specific context.

Common Patterns

• Language/framework: "TypeScript strict. React 19."
• Testing: "Jest/Vitest. Aim for 80% coverage on new code."
• Security: "No hardcoded secrets. Use env vars."
• Architecture: "Feature folders. No circular imports."

Next Steps

• How to use Cursor — Cursor basics.
• Cursor review 2026 — Full Cursor assessment.
• Cursor — Tool page.