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

Understanding AI Agent Context Files

Modern AI coding agents like Claude Code and Cursor can read special context files from your project to understand your codebase, coding conventions, and project requirements. These files are essential for getting consistent, high-quality code from AI assistants.

The two most important context file formats are CLAUDE.md (for Claude Code) and .cursorrules (for Cursor). While they serve similar purposes, they have different formats, capabilities, and best practices.

What is CLAUDE.md?

CLAUDE.md is a markdown file that Claude Code (Anthropic's official CLI tool) reads to understand your project. It's placed in your project root and contains information about your project structure, coding conventions, and any specific instructions for Claude.

Key characteristics of CLAUDE.md:

• Markdown format - supports headings, lists, code blocks, and rich formatting
• Placed in project root as CLAUDE.md
• Read automatically by Claude Code on every interaction
• Can include code examples, file structure, and detailed instructions
• Supports longer, more detailed context than most other formats

What is .cursorrules?

.cursorrules is a configuration file used by Cursor (the AI-first code editor) to understand your project and coding preferences. It uses a more structured format and is specifically optimized for Cursor's features.

Key characteristics of .cursorrules:

• Plain text or structured format
• Placed in project root as .cursorrules
• Read automatically by Cursor
• Often more concise and rule-focused
• Optimized for Cursor's composer and chat features

Key Differences

While both files serve to provide context to AI agents, they have several important differences:

Format and Structure

CLAUDE.md uses full Markdown, allowing for rich documentation with code blocks, headings, and detailed explanations. It reads more like documentation. .cursorrules tends to be more concise and rule-based, focusing on specific instructions rather than explanations.

Verbosity

CLAUDE.md typically contains more detailed information - project architecture, API documentation, coding standards with examples, and comprehensive guidelines. .cursorrules is usually more terse, with focused rules and preferences.

Tool Compatibility

CLAUDE.md is specifically for Claude Code (the CLI). .cursorrules is specifically for Cursor. If you use both tools, you'll want both files in your project.

What to Include in CLAUDE.md

A well-structured CLAUDE.md typically includes:

1. Project Overview - What the project does and its core purpose
2. Tech Stack - Languages, frameworks, and key dependencies
3. Project Structure - Directory layout and file organization
4. Coding Conventions - Naming, formatting, and style preferences
5. Architecture Decisions - Key technical choices and their rationale
6. API Patterns - How endpoints are structured and authenticated
7. Testing Approach - How tests should be written and organized
8. Common Tasks - Frequent operations and how to perform them

What to Include in .cursorrules

Effective .cursorrules files typically contain:

1. Code style preferences (formatting, naming conventions)
2. Framework-specific patterns to follow
3. Error handling approaches
4. Import organization rules
5. Testing requirements
6. Documentation standards
7. Forbidden patterns or anti-patterns to avoid

When to Use Each

Use CLAUDE.md when:

• You're using Claude Code as your primary AI coding tool
• You need detailed documentation and context
• Your project has complex architecture that requires explanation
• You want to include code examples and patterns

Use .cursorrules when:

• You're using Cursor as your primary editor
• You want concise, rule-based instructions
• You need quick configuration without lengthy documentation
• Your team primarily works in Cursor

Use both when:

• Your team uses both Claude Code and Cursor
• You want maximum compatibility with AI tools
• You're generating specs with Keeborg (which creates both automatically)

Generating Context Files Automatically

Writing context files manually can be time-consuming, especially for new projects. Tools like Keeborg can generate both CLAUDE.md and .cursorrules automatically from your project description.

When you describe your app idea to Keeborg, it generates optimized context files that include:

• Project overview and architecture based on your description
• Tech stack recommendations with rationale
• Coding conventions appropriate for your chosen technologies
• API patterns based on your OpenAPI specification
• Database context from your schema
• Integration points and external services

Best Practices

Regardless of which file you use, follow these best practices:

1. Keep it updated - Update context files as your project evolves
2. Be specific - Vague instructions lead to inconsistent results
3. Include examples - Show the AI what good code looks like
4. Document decisions - Explain why, not just what
5. Test your context - Verify the AI follows your guidelines

CLAUDE.md vs .cursorrules vs agents.md: behaviour across tools

The three files do the same job — hand an AI coding agent the context it needs — but each tool reads a different file, and the differences matter once you work across more than one agent.

Cursor

.cursorrules lives in your project root, and newer Cursor versions also read scoped rule files under .cursor/rules. The rules are injected into the model's context on every request, so they shape inline completions, chat, and Cursor's agent mode alike. Keep them short and imperative — long rule files dilute the signal.

Claude Code

Claude Code reads CLAUDE.md from the working directory, merging any CLAUDE.md files it finds up the tree plus a personal one in your home config. It treats the file as standing instructions for the whole session: build commands, conventions, and the things you don't want it to touch. Because Claude Code runs as an agent in your terminal, CLAUDE.md tends to carry more operational detail — test commands, file layout, guardrails — than a typical .cursorrules.

Codex and agents.md

agents.md (often written AGENTS.md) is a tool-neutral convention rather than one vendor's file. Agents such as OpenAI's Codex CLI look for it, and the appeal is portability: one file any compliant agent can read, instead of a separate file per tool. If you switch agents often, agents.md is the lowest-maintenance home for shared instructions.

Which file should you use?

Match the file to the agent you actually run:

• Use CLAUDE.md if Claude Code is your main agent — it's the file Claude Code reads first.
• Use .cursorrules (or .cursor/rules) if your team lives in Cursor.
• Use agents.md if you switch between agents or want one portable instructions file.
• Running more than one agent? Keep a single source of truth and generate the others from it, so the instructions never drift apart.

Two real-world config examples

Example 1: a CLAUDE.md for a Next.js + TypeScript project

# Project: Acme Dashboard

## Stack
Next.js (App Router), TypeScript, Tailwind, Sanity CMS.

## Commands
- Build: npm run build
- Typecheck: npm run typecheck
- Test: npm test

## Conventions
- Server components by default; add 'use client' only when a component needs state or effects.
- Co-locate tests next to the file under test.

## Do not touch
- Generated files in /sanity/types
- Anything under /legacy

Example 2: the same rules as a .cursorrules

You are working on Acme Dashboard: Next.js App Router, TypeScript, Tailwind, Sanity.
- Prefer server components; only use 'use client' when a component needs state or effects.
- Use npm run build and npm run typecheck to verify changes.
- Never edit /sanity/types or /legacy.
Keep changes minimal and match the surrounding code style.

The content is nearly identical — only the framing changes. That's exactly why teams running both tools generate one file from the other instead of editing each by hand.

Keeping CLAUDE.md and .cursorrules in sync

If you run Claude Code and Cursor on the same codebase, you don't want to maintain two rule files by hand. They drift within a week — someone tightens a lint rule in .cursorrules, forgets CLAUDE.md, and the two agents start behaving differently on the same repo. The fix is to treat one file as the source of truth and derive the rest.

Pick a source of truth

Choose the file for the agent your team uses most and make it canonical. Everything else is generated from it, never edited directly. That single decision removes most sync problems before they start.

A sync workflow that holds up

1. Keep the canonical file (say CLAUDE.md) in the repo root and treat edits to it as the only place rules change.
2. Generate .cursorrules and agents.md from it instead of copy-pasting — the content is nearly identical, only the framing differs.
3. Regenerate on every rules change and commit all files in the same PR, so the agents never fall out of alignment.
4. Add a pre-commit hook or CI check that fails when a derived file is out of date with the source.

The mechanical part — turning a CLAUDE.md into a matching .cursorrules — is exactly what a generator is for. Point it at your canonical file and let it emit the others on each change, and the drift disappears entirely.

What to check after a sync

• Both files reference the same directory layout, scripts, and conventions.
• Tool-specific sections — Cursor's terser rules, CLAUDE.md's prose — still read correctly in isolation.
• No stale rule survives in a derived file after you removed it from the source.

More FAQs: agents.md vs CLAUDE.md vs .cursorrules

Is agents.md the same as CLAUDE.md?

No. They serve the same purpose — instructions for an AI coding agent — but CLAUDE.md is the file Claude Code reads, while agents.md is a tool-neutral convention that several agents support. The content can be almost identical; the filename is what each tool looks for.

Can I use CLAUDE.md and .cursorrules in the same repo?

Yes, and many teams do. Claude Code reads CLAUDE.md and Cursor reads .cursorrules, so they don't conflict. The real risk is drift — keep one as the source of truth and regenerate the other when it changes.

Does .cursorrules still work, or do I need .cursor/rules?

Both work. .cursorrules in the project root is still supported, and newer Cursor versions also read scoped rule files under .cursor/rules. Use the scoped folder when you want different rules for different parts of a large codebase.

agents.md vs claude.md vs .cursorrules: which is the standard?

There isn't a single winner yet. CLAUDE.md and .cursorrules are tied to specific tools; agents.md is the closest thing to a vendor-neutral standard. For a deeper side-by-side, see our guide on agents.md vs CLAUDE.md vs .cursorrules. Pick based on the agent you use most, and link them to a generator so adding the others is trivial.

Does Cursor read CLAUDE.md?

Not by default. Cursor reads .cursorrules (and the newer .cursor/rules/ directory), not CLAUDE.md. If your canonical file is CLAUDE.md, generate a .cursorrules from it so Cursor picks up the same rules — it won't parse the CLAUDE.md file on its own.

.cursorrules vs CLAUDE.md — which should I start with?

Start with the file for the agent you use most, then derive the other. If your team lives in Claude Code, make CLAUDE.md canonical; if it's Cursor, start from .cursorrules. The rules are portable — the starting point just decides which file you hand-edit.

Conclusion

Both CLAUDE.md and .cursorrules are essential for getting the most out of AI coding agents. While they serve different tools, the underlying principle is the same: give your AI assistant the context it needs to write code that matches your project's standards and requirements.

If you're starting a new project or want to improve your AI coding workflow, consider using Keeborg to generate both files automatically along with all your other technical specifications. It's the fastest way to set up a spec-driven development workflow.