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 pagesImplementing data fetching (client or server-side)Reviewing code for performance issuesRefactoring existing React/Next.js codeOptimizing bundle size or load timesRule 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 content2. 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 speed3. 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 operations4. Client-Side Data Fetching (MEDIUM-HIGH)
`client-swr-dedup` - Use SWR for automatic request deduplication`client-event-listeners` - Deduplicate global event listeners5. 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 updates6. 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 conditionals7. 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 immutability8. Advanced Patterns (LOW)
`advanced-event-handler-refs` - Store event handlers in refs`advanced-use-latest` - useLatest for stable callback refsHow to Use
Read individual rule files for detailed explanations and code examples:
```
rules/async-parallel.md
rules/bundle-barrel-imports.md
rules/_sections.md
```
Each rule file contains:
Brief explanation of why it mattersIncorrect code example with explanationCorrect code example with explanationAdditional context and referencesFull Compiled Document
For the complete guide with all rules expanded: `AGENTS.md`