# react

A Cursor rule that pins down React conventions for a team: pure components, hook rules, feature-based structure. Useful when an AI agent writes code in its own style.

- rule · `type=rule` · Cursor · ★ 3579
- Author: sanjeed5
- License: CC0-1.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/sanjeed5/awesome-cursor-rules-mdc/tree/HEAD/rules-mdc/react.mdc
- Updated: 2026-05-19
- HTML: https://affpapa.org/en/nevibecode/rules/sanjeed5-react

## What it does

The file `.cursor/rules/react.mdc` plugs into Cursor and fires on `**/*.{jsx,tsx}`. Inside is a set of standards split into sections: component purity and the Rules of Hooks, code organization and naming, smart versus presentational components, state management, performance work. Each point comes with a bad and a good example.

The agent gets concrete targets. Hooks stay at the top level, data is sorted immutably through `useMemo`, state moves up or into Context API instead of being drilled through three layers. For complex global state the rule suggests starting with `useState` and `useReducer`, and reaching for Zustand or Redux Toolkit later.

Optimization should follow profiling, not precede it — `React.memo` and `useCallback` are applied where they pay off. Watch the dependency arrays in `useCallback`: the stale-closure example shows where this usually breaks. The rule assumes TypeScript and `.tsx` components.

## Install

### Cursor (native platform)

**Manually: put the files in place**
- File: `.cursor/rules/react.mdc` — Frontmatter: description, globs, alwaysApply

### Claude Code

**Manually: put the files in place**
- File: `.claude/rules/react.md` — The paths frontmatter field limits the files: move globs from the source into paths

### Codex

**AGENTS.md**
- Codex reads AGENTS.md: paste the rule text there

### GitHub Copilot

**Manually: put the files in place**
- File: `.github/instructions/react.instructions.md` — The applyTo field sets which files it applies to: move globs from the source into applyTo

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/rules/react.md`

### Cline

**Manually: put the files in place**
- File: `.clinerules/react.md`

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/sanjeed5/awesome-cursor-rules-mdc/tree/HEAD/rules-mdc/react.mdc

## When to use it
- settle on one React style across a team
- tell the agent when `useMemo` earns its keep
- split a project into features instead of a flat components folder
- stop drilling props through several layers
- catch a stale closure in `useCallback`

## Example prompts
- Refactor ProductList so it doesn't sort the array during render
- Reorganize the components folder by feature, following the react rule
- Check the useCallback dependencies in this file

## Source text · react.mdc · CC0-1.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: a2af2c7227d2673d.

BEGIN THIRD-PARTY FILE a2af2c7227d2673d
````text
---
description: Definitive guidelines for writing idiomatic, maintainable, and performant React applications using modern best practices and TypeScript.
globs: **/*.{jsx,tsx}
---
# react Best Practices

This guide outlines the non-negotiable standards for building React applications within our team. Adherence ensures predictable behavior, simplifies debugging, and enables future optimizations.

## 1. Core React Principles: Purity & Rules of Hooks

Components and Hooks **must be pure**. They should always return the same output given the same inputs (props, state, context) and not cause side effects during rendering. Obey the [Rules of Hooks](https://react.dev/reference/rules/rules-of-hooks) without exception.

### ❌ BAD: Impure component / Side effect in render
```tsx
function ProductList({ products }) {
  // ❌ Modifies external data during render
  products.sort((a, b) => a.name.localeCompare(b.name));
  return (/* ... */);
}

function MyComponent() {
  // ❌ Hook called conditionally
  if (Math.random() > 0.5) {
    const [count, setCount] = useState(0);
  }
  return (/* ... */);
}
```

### ✅ GOOD: Pure component / Correct Hook usage
```tsx
import { useMemo, useState } from 'react';

function ProductList({ products }) {
  // ✅ Sort data immutably or memoize if expensive
  const sortedProducts = useMemo(() => 
    [...products].sort((a, b) => a.name.localeCompare(b.name)),
    [products]
  );
  return (/* ... */);
}

function MyComponent() {
  // ✅ Hooks always at the top level
  const [count, setCount] = useState(0); 
  // ... conditional logic after hooks
  return (/* ... */);
}
```

## 2. Code Organization & Naming

Organize code by **feature** using the `bulletproof-react` pattern. Use TypeScript (`.tsx`) for all components.

*   **One Component Per File**: Except for small, pure, stateless components closely related to a parent.
*   **Naming**:
    *   Components: `PascalCase` (e.g., `UserProfile.tsx`)
    *   Custom Hooks: `use` prefix + `PascalCase` (e.g., `useAuth.ts`)
    *   Functions/Variables: `camelCase`
    *   CSS Classes: `kebab-case` (via CSS Modules or utility classes)

### ✅ GOOD: Feature-based structure
```
src/
├── features/
│   ├── auth/
│   │   ├── components/
│   │   │   ├── LoginForm.tsx
│   │   │   └── AuthButton.tsx
│   │   ├── hooks/
│   │   │   └── useAuth.ts
│   │   └── api/auth.ts
│   └── products/
│       ├── components/
│       │   ├── ProductCard.tsx
│       │   └── ProductList.tsx
│       └── hooks/useProducts.ts
├── components/ui/  // Reusable, generic UI components
│   ├── Button.tsx
│   └── Modal.tsx
└── App.tsx
```

## 3. Component Design & Patterns

Prioritize **function components with Hooks**. Separate concerns into "smart" (data/logic) and "dumb" (presentational) components.

### ❌ BAD: Class components / Mixed concerns
```tsx
// ❌ Class component (avoid)
class UserProfile extends React.Component { /* ... */ }

// ❌ Component fetches data AND renders complex UI
function ProductPage() {
  const [products, setProducts] = useState([]);
  useEffect(() => { /* fetch products */ }, []);
  return (/* complex product list UI */);
}
```

### ✅ GOOD: Function components / Separation of concerns
```tsx
// ✅ Use function components with hooks
function UserProfile({ user }) { /* ... */ }

// ✅ Smart component (container) handles data fetching
function ProductListContainer() {
  const { products, isLoading } = useProducts(); // Custom hook for data
  if (isLoading) return <LoadingSpinner />;
  return <ProductList products={products} />; // Renders dumb component
}

// ✅ Dumb component (presentational) focuses on UI
function ProductList({ products }) {
````
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