vercel-react-best-practices

name: vercel-react-best-practices description: React and Next.js performance optimization guidelines from Vercel Engineering. This skill should be used when writing, reviewing, or refactoring React/Next.js code to ensure optimal performance patterns. Triggers on tasks involving React components, Next.js pages, data fetching, bundle optimization, or performance improvements.

Vercel React Best Practices

Comprehensive performance optimization guide for React and Next.js applications, maintained by Vercel Engineering. Contains 57 rules across 8 categories, prioritized by impact to guide automated refactoring and code generation.

Loading the Full Guide

The complete rules document with all code examples is maintained at:

https://raw.githubusercontent.com/vercel-labs/agent-skills/main/skills/react-best-practices/AGENTS.md

When you need detailed rule guidance, fetch the full document from the URL above using your web fetch tool. The document is ~80KB and contains all 57 rules with incorrect/correct code examples.

For individual rules, fetch:

https://raw.githubusercontent.com/vercel-labs/agent-skills/main/skills/react-best-practices/rules/{rule-name}.md

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

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-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 SWR for automatic request deduplication
• client-event-listeners — Deduplicate global event listeners
• 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-dependencies — Use primitive dependencies in effects
• rerender-derived-state — Subscribe to derived booleans, not raw values
• 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
• 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-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-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
• advanced-use-latest — useLatest for stable callback refs

How to Use

When a user asks about React/Next.js performance, or when writing/reviewing React code:

1. Identify the relevant category from the priority table above
2. Fetch the specific rule from GitHub for detailed guidance:

   https://raw.githubusercontent.com/vercel-labs/agent-skills/main/skills/react-best-practices/rules/{rule-name}.md
   

3. Or fetch the full guide for comprehensive review:

   https://raw.githubusercontent.com/vercel-labs/agent-skills/main/skills/react-best-practices/AGENTS.md
   

4. Apply the rule's correct pattern, explaining why it matters

Each rule file contains:

• Brief explanation of why it matters
• Incorrect code example with explanation
• Correct code example with explanation
• Additional context and references

Source

Maintained by Vercel Engineering at github.com/vercel-labs/agent-skills.