Cursor Rules Config

Configure project-specific AI behavior through Cursor's rules system. The modern approach uses .cursor/rules/*.mdc files; the legacy .cursorrules file is still supported but deprecated.

Rules System Architecture

Modern Project Rules (.cursor/rules/*.mdc)

Each .mdc file contains YAML frontmatter followed by markdown content:

---
description: "Enforce TypeScript strict mode and functional patterns"
globs: "src/**/*.ts,src/**/*.tsx"
alwaysApply: false
---
# TypeScript Standards

- Use `const` over `let`, never `var`
- Prefer pure functions over classes
- All functions must have explicit return types
- Use discriminated unions over enums

Frontmatter fields:

Field	Type	Purpose
description	string	Concise rule purpose (shown in Cursor UI)
globs	string	Gitignore-style patterns for auto-attachment
alwaysApply	boolean	true = always active; false = only when matching files referenced

Rule Types by alwaysApply + globs Combination

alwaysApply	globs	Behavior
true	empty	Always injected into every prompt
false	set	Auto-attached when matching files are in context
false	empty	Manual only -- reference with @Cursor Rules in chat

File Naming Convention

Use kebab-case with .mdc extension. Names should describe the rule's scope:

.cursor/rules/
  typescript-standards.mdc
  react-component-patterns.mdc
  api-error-handling.mdc
  testing-conventions.mdc
  database-migrations.mdc
  security-requirements.mdc

Create new rules via: Cmd+Shift+P > New Cursor Rule

Complete Project Rules Example

.cursor/rules/project-context.mdc (always-on):

---
description: "Core project context and conventions"
globs: ""
alwaysApply: true
---
# Project: E-Commerce Platform

Tech stack: Next.js 15, TypeScript 5.7, Prisma ORM, PostgreSQL, Tailwind CSS 4.
Package manager: pnpm. Monorepo with turborepo.

## Conventions
- API routes in `app/api/` using Route Handlers
- Server Components by default, `"use client"` only when needed
- Error boundaries at layout level
- All monetary values stored as integers (cents)
- Dates stored as UTC, displayed in user timezone

.cursor/rules/react-patterns.mdc (glob-scoped):

---
description: "React component standards for TSX files"
globs: "src/**/*.tsx,app/**/*.tsx"
alwaysApply: false
---
# React Component Rules

- Export components as named exports, not default
- Props interface named `{Component}Props`
- Use `forwardRef` for components accepting `ref`
- Colocate styles in `.module.css` files
- Server Components: no `useState`, `useEffect`, or event handlers

```tsx
// Correct pattern
export interface ButtonProps {
  variant: 'primary' | 'secondary';
  children: React.ReactNode;
  onClick?: () => void;
}

export function Button({ variant, children, onClick }: ButtonProps) {
  return (
    <button className={styles[variant]} onClick={onClick}>
      {children}
    </button>
  );
}

**`.cursor/rules/api-routes.mdc`** (glob-scoped):
```yaml
---
description: "API route handler patterns"
globs: "app/api/**/*.ts"
alwaysApply: false
---
# API Route Standards

- Always validate request body with Zod
- Return typed `NextResponse.json()` responses
- Use consistent error response shape: `{ error: string, code: string }`
- Wrap handlers in try/catch with structured logging

```ts
import { NextRequest, NextResponse } from 'next/server';
import { z } from 'zod';

const CreateOrderSchema = z.object({
  items: z.array(z.object({
    productId: z.string().uuid(),
    quantity: z.number().int().positive(),
  })),
});

export async function POST(req: NextRequest) {
  try {
    const body = await req.json();
    const parsed = CreateOrderSchema.parse(body);
    const order = await createOrder(parsed);
    return NextResponse.json(order, { status: 201 });
  } catch (err) {
    if (err instanceof z.ZodError) {
      return NextResponse.json(
        { error: 'Validation failed', code: 'INVALID_INPUT', details: err.issues },
        { status: 400 }
      );
    }
    return NextResponse.json(
      { error: 'Internal server error', code: 'INTERNAL_ERROR' },
      { status: 500 }
    );
  }
}

## Legacy .cursorrules Format

Place a `.cursorrules` file in project root. Plain markdown, no frontmatter:

```markdown
# Project Rules

You are working on a Django REST Framework API.

## Stack
- Python 3.12, Django 5.1, DRF 3.15
- PostgreSQL 16 with pgvector extension
- Redis for caching and Celery broker
- pytest for testing

## Conventions
- ViewSets over function-based views
- Always use serializer validation
- Custom exceptions inherit from `APIException`
- All endpoints require authentication unless explicitly marked
- Use `select_related` and `prefetch_related` to avoid N+1 queries

## Code Style
- Type hints on all function signatures
- Docstrings on all public methods (Google style)
- Max function length: 30 lines

Migration: .cursorrules to .cursor/rules/

Split a monolithic .cursorrules into scoped .mdc files:

1. Create .cursor/rules/ directory
2. Extract global context into an alwaysApply: true rule
3. Extract language/framework rules into glob-scoped rules
4. Delete .cursorrules after verifying all rules load

Referencing Files in Rules

Use @file syntax to include additional context files when a rule is applied:

---
description: "Database schema context for migration files"
globs: "prisma/**/*.prisma,drizzle/**/*.ts"
alwaysApply: false
---
Reference these files for schema context:
@prisma/schema.prisma
@docs/data-model.md

Debugging Rules

1. Open Chat and type @Cursor Rules to see which rules are active
2. Check glob patterns match your files: open a file, then verify the rule appears in context pills
3. Rules with alwaysApply: true always show; glob rules only appear when matching files are in context

Enterprise Considerations

• Version control: Commit .cursor/rules/ to git -- rules are project documentation
• Team alignment: Use alwaysApply: true for team-wide standards
• Sensitive data: Never put API keys, secrets, or credentials in rules files
• Rule size: Keep individual rules focused and under 200 lines; split large rules into multiple files
• Audit trail: Rules changes appear in git history for compliance review

Resources

• Cursor Rules Documentation
• MDC Rules Deep Dive
• awesome-cursorrules