vercel-react-best-practices

by vercel

React and Next.js performance optimization guidelines from Vercel Engineering. This skill should be used when writing, reviewing, or refactoring React/Next.js… npx skills add https://github.com/vercel-labs/cursor-plugin --skill vercel-react-best-practices Download ZIPGitHub8

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

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-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

Source

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

How to Use

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

• Identify the relevant category from the priority table above

• 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

• Or fetch the full guide for comprehensive review:

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

• 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