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Claude Agent Skill · by Vercel Labs

Vercel React Best Practices

This is Vercel's internal performance playbook turned into actionable code guidance. It runs 69 specific checks across React and Next.js codebases, catching thi

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Terminal · npx
$npx skills add https://github.com/vercel-labs/agent-skills --skill vercel-react-best-practices
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Vercel React Best Practices drops into any Paperclip agent that handles this kind of work. Assign it to a specialist inside a pre-configured PaperclipOrg company and the skill becomes available on every heartbeat — no prompt engineering, no tool wiring.

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SKILL.md149 lines
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---name: vercel-react-best-practicesdescription: 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.license: MITmetadata:  author: vercel  version: "1.0.0"--- # Vercel React Best Practices Comprehensive performance optimization guide for React and Next.js applications, maintained by Vercel. Contains 70 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-cheap-condition-before-await` - Check cheap sync conditions before awaiting flags or remote values- `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-analyzable-paths` - Prefer statically analyzable import and file-system paths to avoid broad bundles and traces- `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-hoist-static-io` - Hoist static I/O (fonts, logos) to module level- `server-no-shared-module-state` - Avoid module-level mutable request state in RSC/SSR- `server-serialization` - Minimize data passed to client components- `server-parallel-fetching` - Restructure components to parallelize fetches- `server-parallel-nested-fetching` - Chain nested fetches per item in Promise.all- `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-split-combined-hooks` - Split hooks with independent dependencies- `rerender-move-effect-to-event` - Put interaction logic in event handlers- `rerender-transitions` - Use startTransition for non-urgent updates- `rerender-use-deferred-value` - Defer expensive renders to keep input responsive- `rerender-use-ref-transient-values` - Use refs for transient frequent values- `rerender-no-inline-components` - Don't define components inside components ### 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- `rendering-resource-hints` - Use React DOM resource hints for preloading- `rendering-script-defer-async` - Use defer or async on script tags ### 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- `js-flatmap-filter` - Use flatMap to map and filter in one pass- `js-request-idle-callback` - Defer non-critical work to browser idle time ### 8. Advanced Patterns (LOW) - `advanced-effect-event-deps` - Don't put `useEffectEvent` results in effect deps- `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 Read individual rule files for detailed explanations and code examples: ```rules/async-parallel.mdrules/bundle-barrel-imports.md``` Each rule file contains:- Brief explanation of why it matters- Incorrect code example with explanation- Correct code example with explanation- Additional context and references ## Full Compiled Document For the complete guide with all rules expanded: `AGENTS.md`