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 usedasync-parallel - Use Promise.all() for independent operationsasync-dependencies - Use better-all for partial dependenciesasync-api-routes - Start promises early, await late in API routesasync-suspense-boundaries - Use Suspense to stream content
2. Bundle Size Optimization (CRITICAL)
bundle-barrel-imports - Import directly, avoid barrel filesbundle-dynamic-imports - Use next/dynamic for heavy componentsbundle-defer-third-party - Load analytics/logging after hydrationbundle-conditional - Load modules only when feature is activatedbundle-preload - Preload on hover/focus for perceived speed
3. Server-Side Performance (HIGH)
server-cache-react - Use React.cache() for per-request deduplicationserver-cache-lru - Use LRU cache for cross-request cachingserver-serialization - Minimize data passed to client componentsserver-parallel-fetching - Restructure components to parallelize fetchesserver-after-nonblocking - Use after() for non-blocking operations
4. Client-Side Data Fetching (MEDIUM-HIGH)
client-swr-dedup - Use SWR for automatic request deduplicationclient-event-listeners - Deduplicate global event listeners
5. Re-render Optimization (MEDIUM)
rerender-defer-reads - Don't subscribe to state only used in callbacksrerender-memo - Extract expensive work into memoized componentsrerender-dependencies - Use primitive dependencies in effectsrerender-derived-state - Subscribe to derived booleans, not raw valuesrerender-functional-setstate - Use functional setState for stable callbacksrerender-lazy-state-init - Pass function to useState for expensive valuesrerender-transitions - Use startTransition for non-urgent updates
6. Rendering Performance (MEDIUM)
rendering-animate-svg-wrapper - Animate div wrapper, not SVG elementrendering-content-visibility - Use content-visibility for long listsrendering-hoist-jsx - Extract static JSX outside componentsrendering-svg-precision - Reduce SVG coordinate precisionrendering-hydration-no-flicker - Use inline script for client-only datarendering-activity - Use Activity component for show/hiderendering-conditional-render - Use ternary, not && for conditionals
7. JavaScript Performance (LOW-MEDIUM)
js-batch-dom-css - Group CSS changes via classes or cssTextjs-index-maps - Build Map for repeated lookupsjs-cache-property-access - Cache object properties in loopsjs-cache-function-results - Cache function results in module-level Mapjs-cache-storage - Cache localStorage/sessionStorage readsjs-combine-iterations - Combine multiple filter/map into one loopjs-length-check-first - Check array length before expensive comparisonjs-early-exit - Return early from functionsjs-hoist-regexp - Hoist RegExp creation outside loopsjs-min-max-loop - Use loop for min/max instead of sortjs-set-map-lookups - Use Set/Map for O(1) lookupsjs-tosorted-immutable - Use toSorted() for immutability
8. Advanced Patterns (LOW)
advanced-event-handler-refs - Store event handlers in refsadvanced-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)
const user = await fetchUser()
const posts = await fetchPosts()
const comments = await fetchComments()
const [user, posts, comments] = await Promise.all([
fetchUser(),
fetchPosts(),
fetchComments()
])
Avoid Barrel File Imports (CRITICAL)
import { Check, X, Menu } from 'lucide-react'
import Check from 'lucide-react/dist/esm/icons/check'
import X from 'lucide-react/dist/esm/icons/x'
Dynamic Imports for Heavy Components (CRITICAL)
import { MonacoEditor } from './monaco-editor'
import dynamic from 'next/dynamic'
const MonacoEditor = dynamic(
() => import('./monaco-editor').then(m => m.MonacoEditor),
{ ssr: false }
)
Use Functional setState (MEDIUM)
const addItems = useCallback((newItems) => {
setItems([...items, ...newItems])
}, [items])
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
Metadata
Version
- Current Version: 1.0.0
- Last Updated: 2026-01-22
- Compatible Platforms: Claude, ChatGPT, Gemini
- Original Source: vercel/agent-skills
Related Skills
Tags
#React #Next.js #performance #optimization #vercel #waterfalls #bundle-size #RSC #frontend
