vercel-react-best-practices

SKILL.md

Vercel React Best Practices

Comprehensive performance optimization guide for React and Next.js applications, maintained by Vercel. Contains 45 rules across 8 categories, prioritized by impact to guide automated refactoring and code generation.

When to Apply

Reference these guidelines when:

Writing new React components or Next.js pages

Implementing data fetching (client or server-side)

Reviewing code for performance issues

Refactoring existing React/Next.js code

Optimizing bundle size or load times

Rule Categories by Priority

Priority
Category
Impact
Prefix

1
Eliminating Waterfalls
CRITICAL
async-

2
Bundle Size Optimization
CRITICAL
bundle-

3
Server-Side Performance
HIGH
server-

4
Client-Side Data Fetching
MEDIUM-HIGH
client-

5
Re-render Optimization
MEDIUM
rerender-

6
Rendering Performance
MEDIUM
rendering-

7
JavaScript Performance
LOW-MEDIUM
js-

8
Advanced Patterns
LOW
advanced-

Quick Reference

1. Eliminating Waterfalls (CRITICAL)

async-defer-await - Move await into branches where actually used

async-parallel - Use Promise.all() for independent operations

async-dependencies - Use better-all for partial dependencies

async-api-routes - Start promises early, await late in API routes

async-suspense-boundaries - Use Suspense to stream content

2. Bundle Size Optimization (CRITICAL)

bundle-barrel-imports - Import directly, avoid barrel files

bundle-dynamic-imports - Use next/dynamic for heavy components

bundle-defer-third-party - Load analytics/logging after hydration

bundle-conditional - Load modules only when feature is activated

bundle-preload - Preload on hover/focus for perceived speed

3. Server-Side Performance (HIGH)

server-cache-react - Use React.cache() for per-request deduplication

server-cache-lru - Use LRU cache for cross-request caching

server-serialization - Minimize data passed to client components

server-parallel-fetching - Restructure components to parallelize fetches

server-after-nonblocking - Use after() for non-blocking operations

4. Client-Side Data Fetching (MEDIUM-HIGH)

client-swr-dedup - Use SWR for automatic request deduplication

client-event-listeners - Deduplicate global event listeners

5. Re-render Optimization (MEDIUM)

rerender-defer-reads - Don't subscribe to state only used in callbacks

rerender-memo - Extract expensive work into memoized components

rerender-dependencies - Use primitive dependencies in effects

rerender-derived-state - Subscribe to derived booleans, not raw values

rerender-functional-setstate - Use functional setState for stable callbacks

rerender-lazy-state-init - Pass function to useState for expensive values

rerender-transitions - Use startTransition for non-urgent updates

6. Rendering Performance (MEDIUM)

rendering-animate-svg-wrapper - Animate div wrapper, not SVG element

rendering-content-visibility - Use content-visibility for long lists

rendering-hoist-jsx - Extract static JSX outside components

rendering-svg-precision - Reduce SVG coordinate precision

rendering-hydration-no-flicker - Use inline script for client-only data

rendering-activity - Use Activity component for show/hide

rendering-conditional-render - Use ternary, not && for conditionals

7. JavaScript Performance (LOW-MEDIUM)

js-batch-dom-css - Group CSS changes via classes or cssText

js-index-maps - Build Map for repeated lookups

js-cache-property-access - Cache object properties in loops

js-cache-function-results - Cache function results in module-level Map

js-cache-storage - Cache localStorage/sessionStorage reads

js-combine-iterations - Combine multiple filter/map into one loop

js-length-check-first - Check array length before expensive comparison

js-early-exit - Return early from functions

js-hoist-regexp - Hoist RegExp creation outside loops

js-min-max-loop - Use loop for min/max instead of sort

js-set-map-lookups - Use Set/Map for O(1) lookups

js-tosorted-immutable - Use toSorted() for immutability

8. Advanced Patterns (LOW)

advanced-event-handler-refs - Store event handlers in refs

advanced-use-latest - useLatest for stable callback refs

How to Use

For detailed explanations and code examples, read the full compiled document: AGENTS.md

Each rule contains:

Brief explanation of why it matters

Incorrect code example with explanation

Correct code example with explanation

Additional context and references

Key Examples

Promise.all for Independent Operations (CRITICAL)

// ❌ Sequential: 3 round trips
const user = await fetchUser()
const posts = await fetchPosts()
const comments = await fetchComments()

// ✅ Parallel: 1 round trip
const [user, posts, comments] = await Promise.all([
  fetchUser(),
  fetchPosts(),
  fetchComments()
])

Avoid Barrel File Imports (CRITICAL)

// ❌ Imports entire library (200-800ms import cost)
import { Check, X, Menu } from 'lucide-react'

// ✅ Imports only what you need
import Check from 'lucide-react/dist/esm/icons/check'
import X from 'lucide-react/dist/esm/icons/x'

Dynamic Imports for Heavy Components (CRITICAL)

// ❌ Monaco bundles with main chunk ~300KB
import { MonacoEditor } from './monaco-editor'

// ✅ Monaco loads on demand
import dynamic from 'next/dynamic'
const MonacoEditor = dynamic(
  () => import('./monaco-editor').then(m => m.MonacoEditor),
  { ssr: false }
)

Use Functional setState (MEDIUM)

// ❌ Requires state as dependency, stale closure risk
const addItems = useCallback((newItems) => {
  setItems([...items, ...newItems])
}, [items])

// ✅ Stable callback, no stale closures
const addItems = useCallback((newItems) => {
  setItems(curr => [...curr, ...newItems])
}, [])

Constraints

Required Rules (MUST)

Eliminate waterfalls: Use Promise.all and Suspense

Optimize bundles: No barrel imports, use dynamic imports

RSC boundaries: Serialize only the necessary data

Prohibited Patterns (MUST NOT)

Sequential await: Do not execute independent fetches sequentially

Array mutations: Use toSorted() instead of sort()

Inline objects in React.cache: Causes cache misses

References

React Documentation

Next.js Documentation

SWR

better-all

Vercel Blog: Optimizing Package Imports

Vercel Blog: Dashboard Performance

Metadata

Version

Current Version: 1.0.0

Last Updated: 2026-01-22

Compatible Platforms: Claude, ChatGPT, Gemini

Original Source: vercel/agent-skills

Related Skills

performance-optimization: General performance optimization

state-management: State management

Tags

#React #Next.js #performance #optimization #vercel #waterfalls #bundle-size #RSC #frontend