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Vercel React Best Practices TEXT

Provides 70 prioritized performance optimization rules for React and Next.js applications, covering data fetching, bundle size, rendering, and JavaScript efficiency. It guides the writing, reviewing, and refactoring of code to eliminate waterfalls, reduce re-renders, and optimize load times.

5 uses this weeksource vercel-labslicence MIT

Quality gate: PASS · better answers · measured 2026-10-24
Blind-judged against the bare model on 2 requests: average lift +4.5 points (specificity, structure, method, fit).
won 2/2, lift +4.5, tokens ×65.28

Try asking

Say it in your own words; the assistant finds this recipe by itself. Examples:

“Optimer min Next.js side for at fjerne sekventielle API-kald og hurtiggøre den indledende load.”

“Gennemgå min Dashboard-komponent for unødvendige re-renders og foreslå optimeringer med React.memo.”

“Hvordan bør jeg strukturere data-fetching i App Router for at undgå at blokere hovedtråden?”

“Refactor this Next.js page to eliminate the waterfall of API calls and improve initial load time.”

“Review my Dashboard component for unnecessary re-renders and suggest optimizations using React.memo.”

“How should I structure my data fetching in App Router to avoid blocking the main thread?”

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Good for

reactnextjsperformanceoptimizationbundle-sizerefactoringdata-fetchingbest-practicesvercel

Not for

Do not use this skill for general frontend styling, UI design, or accessibility audits, as it focuses strictly on performance and code structure. It is not suitable for non-React frameworks like Vue or Angular, nor for backend API logic that does not involve React Server Components or client-side React rendering. For general JavaScript syntax errors or basic debugging unrelated to performance, use a standard linter or debugger instead.

Details

When it is the right choice

Use this skill when writing new React components or Next.js pages to ensure they follow optimal performance patterns. It is also essential when reviewing or refactoring existing code to identify and fix performance bottlenecks like unnecessary re-renders, large bundles, or sequential data fetching. Apply it when specifically tasked with improving load times, optimizing bundle size, or implementing efficient data fetching strategies in a React/Next.js stack.

The full recipe the assistant reads

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.md
rules/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

Files in this skill (76)

AGENTS.md
README.md
SKILL.md
metadata.json
rules/_sections.md
rules/_template.md
rules/advanced-effect-event-deps.md
rules/advanced-event-handler-refs.md
rules/advanced-init-once.md
rules/advanced-use-latest.md
rules/async-api-routes.md
rules/async-cheap-condition-before-await.md
rules/async-defer-await.md
rules/async-dependencies.md
rules/async-parallel.md
rules/async-suspense-boundaries.md
rules/bundle-analyzable-paths.md
rules/bundle-barrel-imports.md
rules/bundle-conditional.md
rules/bundle-defer-third-party.md
rules/bundle-dynamic-imports.md
rules/bundle-preload.md
rules/client-event-listeners.md
rules/client-localstorage-schema.md
rules/client-passive-event-listeners.md
rules/client-swr-dedup.md
rules/js-batch-dom-css.md
rules/js-cache-function-results.md
rules/js-cache-property-access.md
rules/js-cache-storage.md
rules/js-combine-iterations.md
rules/js-early-exit.md
rules/js-flatmap-filter.md
rules/js-hoist-regexp.md
rules/js-index-maps.md
rules/js-length-check-first.md
rules/js-min-max-loop.md
rules/js-request-idle-callback.md
rules/js-set-map-lookups.md
rules/js-tosorted-immutable.md
rules/rendering-activity.md
rules/rendering-animate-svg-wrapper.md
rules/rendering-conditional-render.md
rules/rendering-content-visibility.md
rules/rendering-hoist-jsx.md
rules/rendering-hydration-no-flicker.md
rules/rendering-hydration-suppress-warning.md
rules/rendering-resource-hints.md
rules/rendering-script-defer-async.md
rules/rendering-svg-precision.md
rules/rendering-usetransition-loading.md
rules/rerender-defer-reads.md
rules/rerender-dependencies.md
rules/rerender-derived-state-no-effect.md
rules/rerender-derived-state.md
rules/rerender-functional-setstate.md
rules/rerender-lazy-state-init.md
rules/rerender-memo-with-default-value.md
rules/rerender-memo.md
rules/rerender-move-effect-to-event.md
rules/rerender-no-inline-components.md
rules/rerender-simple-expression-in-memo.md
rules/rerender-split-combined-hooks.md
rules/rerender-transitions.md
rules/rerender-use-deferred-value.md
rules/rerender-use-ref-transient-values.md
rules/server-after-nonblocking.md
rules/server-auth-actions.md
rules/server-cache-lru.md
rules/server-cache-react.md
rules/server-dedup-props.md
rules/server-hoist-static-io.md
rules/server-no-shared-module-state.md
rules/server-parallel-fetching.md
rules/server-parallel-nested-fetching.md
rules/server-serialization.md

Where it comes from

Vendored from vercel-labs/agent-skills, commit 063bee94c3f4, path skills/react-best-practices, licence MIT. The upstream licence file ships inside the skill.