Vercel React Best Practices

Comprehensive performance optimization guide for React, React Native, and Next.js applications, maintained by Vercel. Contains 65 rules across 8 categories, prioritized by impact to guide automated refactoring and code generation. Includes platform-specific examples (Web, React Native) and library alternatives (SWR, React Query, Jotai).

When to Apply

Reference these guidelines when:

• Writing new React components, React Native screens, or Next.js pages
• Implementing data fetching (client or server-side) with SWR, React Query, or other libraries
• Reviewing code for performance issues across web and mobile platforms
• Refactoring existing React/React Native/Next.js code
• Optimizing bundle size or load times
• Choosing between framework alternatives (Next.js vs Vite vs CRA)
• Selecting state management or data fetching libraries

Rule Categories by Priority

Priority	Category	Impact	Prefix
0	Hooks & Core Patterns	HIGH	hooks-
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

0. Hooks & Core Patterns (HIGH)

• hooks-builtin-patterns - Correct usage patterns for built-in React hooks

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
• async-use-api - Use React use() API for data and context

2. Bundle Size Optimization (CRITICAL)

• bundle-barrel-imports - Import directly, avoid barrel files
• bundle-avoid-namespace-react - Avoid namespace React imports (import * as React)
• bundle-dynamic-imports - Use dynamic imports for heavy components (next/dynamic or React.lazy)
• bundle-defer-third-party - Load analytics/logging after hydration (next/dynamic or React.lazy)
• bundle-conditional - Load modules only when feature is activated
• bundle-preload - Preload on hover/focus for perceived speed
• bundle-type-imports - Use explicit type imports (import type)

3. Server-Side Performance (HIGH)

• server-auth-actions - Authenticate server actions like API routes
• server-cache-react - Use React.cache() for per-request deduplication
• server-cache-lru - Use LRU cache for cross-request caching
• server-dedup-props - Avoid duplicate serialization in RSC props
• 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 data fetching libraries (React Query or SWR) for automatic deduplication
• client-event-listeners - Deduplicate global event listeners (Jotai or useSWRSubscription)
• client-passive-event-listeners - Use passive listeners for scroll
• client-localstorage-schema - Version and minimize localStorage data

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-memo-with-default-value - Hoist default non-primitive props
• rerender-props-default-values - Hoist default props to avoid re-renders
• rerender-dependencies - Use primitive dependencies in effects
• rerender-derived-state - Subscribe to derived booleans, not raw values (web: useMediaQuery, RN: custom hook)
• rerender-derived-state-no-effect - Derive state during render, not effects
• rerender-functional-setstate - Use functional setState for stable callbacks
• rerender-lazy-state-init - Pass function to useState for expensive values
• rerender-simple-expression-in-memo - Avoid memo for simple primitives
• rerender-move-effect-to-event - Put interaction logic in event handlers
• rerender-transitions - Use startTransition for non-urgent updates (web and React Native)
• rerender-starttransition-patterns - Advanced startTransition patterns and best practices
• rerender-use-ref-transient-values - Use refs for transient frequent values

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-hydration-suppress-warning - Suppress expected mismatches
• rendering-activity - Use Activity component for show/hide
• rendering-conditional-render - Use ternary, not && for conditionals
• rendering-react-dom-apis - Use React DOM APIs correctly
• rendering-usetransition-loading - Prefer useTransition for loading state

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-prefer-dayjs - Prefer Day.js over Moment.js for smaller bundle
• 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-init-once - Initialize app once per app load (module-level let or useRef)
• advanced-use-latest - useLatest for stable callback refs

How to Use

Read individual rule files for detailed explanations and code examples:

rules/async-parallel.md
rules/bundle-barrel-imports.md

Each rule file contains:

• Brief explanation of why it matters
• Incorrect code example with explanation
• Correct code examples with platform/framework/library alternatives:
  • Web (Next.js, Vite, CRA)
  • React Native (where applicable)
  • Library alternatives (SWR vs React Query, Jotai, etc.)
• Additional context and references

Full Compiled Document

For the complete guide with all rules expanded: AGENTS.md