DEV Community

BLNCraft
BLNCraft

Posted on

How We Built 162 Production Rules Files for Claude Code and Cursor (And Why You Should Too)

#cursor #ai #productivity #programming

Cursor 3.3 just shipped parallel agents and worktrees. If you're using AI coding assistants in production, the quality of your rules files is now a multiplier — not just for one agent, but for every parallel agent running in your workspace.

We've been using Claude Code and Cursor daily across a range of projects. Over the past year, we accumulated a library of rules files for 54 dev stacks. We just packaged and released them.

What are CLAUDE.md and .cursorrules files?

CLAUDE.md is the project-level instruction file for Claude Code (Anthropic's CLI coding agent). It's loaded automatically when Claude Code starts a session in your project. You use it to define conventions, patterns, testing requirements, and constraints.

.cursorrules is the equivalent for Cursor IDE. It's loaded by Cursor's AI features (Composer, Chat, Tab) to guide code generation.

Both serve the same purpose: telling the AI how your project works so it generates code that fits your codebase instead of guessing.

Why generic rules don't work

Most rules files you find online are generic:

- Write clean, maintainable code
- Follow best practices
- Add comments where necessary
Enter fullscreen mode Exit fullscreen mode

This is the equivalent of telling a new hire "write good code." It doesn't work because:

  1. Every stack has specific conventions — React hooks have rules, FastAPI has dependency injection patterns, Rust has error handling idioms
  2. Anti-patterns are stack-specific — the things an AI gets wrong in Go are different from what it gets wrong in TypeScript
  3. Your team's conventions matter — snake_case vs camelCase, barrel exports vs direct imports, test file locations

What's in our pack

We built rules files for 54 stacks:

Category Stacks
Frontend React, Next.js, Vue, Svelte, Angular, Astro, Remix, Solid, Qwik
Backend FastAPI, Django, Flask, Express, NestJS, Hono, Rails, Spring Boot, Laravel
Systems Rust, Go, C++, Zig
Mobile React Native, Swift/iOS, Kotlin/Android, Flutter
Infra Docker, Kubernetes, Terraform, Pulumi
Data PostgreSQL, MongoDB, Redis, Prisma, Drizzle
Languages TypeScript, Python, Rust, Go, Java, C#, Ruby, PHP, Elixir

Each stack gets three files:

  • CLAUDE.md — full rules for Claude Code (typically 100-200 lines of specific conventions)
  • .cursorrules — condensed version for Cursor IDE (focused on code generation patterns)
  • README.md — explains what each rule enforces and why

Example: FastAPI CLAUDE.md excerpt 

## API Patterns
- Use Pydantic v2 model_validator instead of root_validator
- Return Pydantic models directly from endpoints, never dict()
- Use Annotated[Depends(...)] for dependency injection
- Async handlers only — no sync def endpoints
- HTTPException for client errors, let unexpected errors propagate

## Testing
- Use httpx.AsyncClient, not TestClient
- Fixtures: db_session, async_client, authenticated_client
- Test file mirrors source: tests/api/test_users.py → src/api/users.py
Enter fullscreen mode Exit fullscreen mode

Compare that to "follow FastAPI best practices." One tells the AI exactly what to do. The other tells it nothing.

How to use them

  1. Download the pack
  2. Find your stack folder
  3. Copy CLAUDE.md to your project root (for Claude Code)
  4. Copy .cursorrules to your project root (for Cursor)
  5. Customize for your team's specific conventions

That's it. No setup, no dependencies. Drop in and go.

The Cursor 3.3 multiplier

With Cursor 3.3's parallel agents, good rules files compound. Each agent that spins up in a worktree loads your .cursorrules. If those rules are specific and accurate, every agent produces code that fits your codebase. If they're generic, you're reviewing and fixing output from multiple agents simultaneously.

162 rules files covering 54 stacks. €29 one-time.

Get the pack on Gumroad →

Top comments (0)