CLAUDE.md vs .cursorrules: What's the Difference (and When to Use Each)

If you're using AI coding tools in 2026, you've probably heard of both .cursorrules and CLAUDE.md. Both files tell your AI what to do. Both can save you hours of re-explaining context. But they're not the same — and using one when you need the other is a slow leak in your productivity.

Here's the practical breakdown.

What .cursorrules Does

.cursorrules is a Cursor-specific config file. It lives at the root of your project and loads automatically when Cursor opens that folder.

Think of it as a project-level system prompt — scoped to one repo, one codebase.

Good uses:

• "This project uses TypeScript strict mode. Never use any."
• "All API calls go through /lib/api.ts. Never fetch directly."
• "Database schema is Prisma. Do not invent new fields — check schema.prisma first."
• "Tests use Vitest, not Jest."

The rule is: .cursorrules is about this project, right now, in Cursor.

What CLAUDE.md Does

CLAUDE.md is a Markdown file that Claude Code reads at startup — from your project root, your home directory, or both. It's Claude's initialization document.

Think of it as a persistent memory file — your preferences, your workflow, your non-negotiables.

Good uses:

• "When I say 'refactor', always preserve the public API."
• "I prefer explicit over implicit. Never add magic."
• "Before modifying any file, read it fully."
• "Use TodoWrite to track tasks. Don't invent task names."

The rule is: CLAUDE.md is about how you work, across projects, in Claude Code.

The Key Difference (One Sentence Each)

.cursorrules → tells Cursor what's true about this codebase
CLAUDE.md → tells Claude how you think and operate

Can You Use Both?

Yes, and you often should.

.cursorrules handles project-specific facts that would change repo to repo. CLAUDE.md handles your personal workflow rules that travel everywhere.

Example setup for a senior developer:

CLAUDE.md (global, in ~/)

You are my senior pair programmer.
I don't want explanations unless I ask.
Read files before modifying them.
Small commits. Atomic changes.
When stuck, say so — don't hallucinate a solution.

.cursorrules (in project root)

Stack: Next.js 15, Tailwind 3, Drizzle ORM, PostgreSQL.
Authentication: Lucia Auth. Never roll your own.
Styling: Use existing components in /components/ui first.
No barrel files (index.ts re-exports). Import directly.

Together, they give the AI a complete picture: who you are AND what this codebase is.

Common Mistakes

1. Putting project facts in CLAUDE.md

If you hardcode your stack in CLAUDE.md, it'll bleed into every other project. Keep project facts in .cursorrules.

2. Putting personal preferences in .cursorrules

Future team members will inherit your .cursorrules. Don't put "I prefer verbose variable names" — put actual project constraints.

3. Writing rules no AI will follow

Both files suffer from the same problem: vague rules get ignored. "Write clean code" does nothing. "No function over 40 lines without a comment" is specific enough to enforce.

4. Never updating them

These files are living documents. Every time you correct an AI mistake, ask: should this be a rule? If it happens twice, add it.

TL;DR

Want to Skip the Setup Time?

Building effective rule files from scratch takes trial and error. I've packaged the best patterns into ready-to-use kits:

Cursor Rules Pack v2 — 45+ production-tested .cursorrules for the most common stacks (Next.js, FastAPI, Django, React Native, and more). Drop them in, customize the stack-specific lines, done.

CLAUDE.md Rules Pack — 30+ CLAUDE.md templates for Claude Code, organized by role (solo dev, lead, freelancer client work). Covers the behavioral patterns that matter most.

Both are $27. Both save hours of iteration.