Vercel React Best Practices

VercelOfficialCreated by vercel

Skill
Guidelines
Software development
MIT
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From the author

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.

— the description by vercel

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides a structured set of 70 rules for React and Next.js development. It categorizes best practices into eight areas, including data fetching, bundle management, server-side operations, and rendering techniques. The guidelines are designed to assist developers in writing and refactoring code by providing specific patterns for common development scenarios.

What it does

Provides 70 distinct rules for React and Next.js development
Categorizes patterns by priority and impact
Offers guidance on eliminating request waterfalls
Details methods for bundle size management
Outlines server-side and client-side data fetching patterns
Suggests techniques for re-render and rendering optimization

When to use it

When writing new React components or Next.js pages
During the implementation of data fetching logic
When reviewing code for adherence to established patterns
When refactoring existing React or Next.js codebases

Advantages

Organized by priority to help focus on high-impact changes
Provides clear prefixes for categorizing rules
Includes specific patterns for both client and server environments
Standardizes development approaches across projects

Usage examples

“How can I improve my data fetching in a Next.js API route?”: The agent will reference the async-api-routes rule to suggest starting promises early and awaiting them late.
“What is the recommended way to handle heavy components in Next.js?”: The agent will point to the bundle-dynamic-imports rule, recommending the use of next/dynamic.

Install

Download the skill as a ZIP:
https://autogineer.com/agent-skills/vercel-labs/vercel-react-best-practices/download

Unzip it into the cross-client skills folder of your project:

mkdir -p .agents/skills && unzip vercel-react-best-practices.zip -d .agents/skills

Documentation by vercel

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

AGENTS.md105.7 KiB
ATTRIBUTION.mdAdded by AutoGineer893 B
README.md3.3 KiB
SKILL.md7.1 KiB
metadata.json921 B
rules/_sections.md1.5 KiB
rules/_template.md631 B
rules/advanced-effect-event-deps.md1.8 KiB
rules/advanced-event-handler-refs.md1.4 KiB
rules/advanced-init-once.md958 B
rules/advanced-use-latest.md1.0 KiB
rules/async-api-routes.md1.1 KiB
rules/async-cheap-condition-before-await.md1.2 KiB
rules/async-defer-await.md2.2 KiB
rules/async-dependencies.md1.3 KiB
rules/async-parallel.md654 B
rules/async-suspense-boundaries.md2.5 KiB
rules/bundle-analyzable-paths.md2.3 KiB
rules/bundle-barrel-imports.md2.7 KiB
rules/bundle-conditional.md949 B
rules/bundle-defer-third-party.md920 B
rules/bundle-dynamic-imports.md791 B
rules/bundle-preload.md1.1 KiB
rules/client-event-listeners.md1.9 KiB
rules/client-localstorage-schema.md1.9 KiB
rules/client-passive-event-listeners.md1.6 KiB
rules/client-swr-dedup.md1.1 KiB
rules/js-batch-dom-css.md3.2 KiB
rules/js-cache-function-results.md1.9 KiB
rules/js-cache-property-access.md532 B
rules/js-cache-storage.md1.6 KiB
rules/js-combine-iterations.md753 B
rules/js-early-exit.md1.1 KiB
rules/js-flatmap-filter.md1.4 KiB
rules/js-hoist-regexp.md1.0 KiB
rules/js-index-maps.md837 B
rules/js-length-check-first.md1.7 KiB
rules/js-min-max-loop.md2.2 KiB
rules/js-request-idle-callback.md2.6 KiB
rules/js-set-map-lookups.md532 B
rules/js-tosorted-immutable.md1.7 KiB
rules/rendering-activity.md564 B
rules/rendering-animate-svg-wrapper.md1.2 KiB
rules/rendering-conditional-render.md980 B
rules/rendering-content-visibility.md815 B
rules/rendering-hoist-jsx.md1.0 KiB
rules/rendering-hydration-no-flicker.md2.3 KiB
rules/rendering-hydration-suppress-warning.md872 B
rules/rendering-resource-hints.md2.5 KiB
rules/rendering-script-defer-async.md1.8 KiB
rules/rendering-svg-precision.md588 B
rules/rendering-usetransition-loading.md2.0 KiB
rules/rerender-defer-reads.md973 B
rules/rerender-dependencies.md824 B
rules/rerender-derived-state-no-effect.md1.2 KiB
rules/rerender-derived-state.md728 B
rules/rerender-functional-setstate.md2.9 KiB
rules/rerender-lazy-state-init.md2.0 KiB
rules/rerender-memo-with-default-value.md1.1 KiB
rules/rerender-memo.md1.1 KiB
rules/rerender-move-effect-to-event.md1.2 KiB
rules/rerender-no-inline-components.md2.1 KiB
rules/rerender-simple-expression-in-memo.md1018 B
rules/rerender-split-combined-hooks.md1.8 KiB
rules/rerender-transitions.md1.0 KiB
rules/rerender-use-deferred-value.md1.8 KiB
rules/rerender-use-ref-transient-values.md1.7 KiB
rules/server-after-nonblocking.md2.0 KiB
rules/server-auth-actions.md2.6 KiB
rules/server-cache-lru.md1.3 KiB
rules/server-cache-react.md2.2 KiB
rules/server-dedup-props.md2.0 KiB
rules/server-hoist-static-io.md4.3 KiB
rules/server-no-shared-module-state.md1.7 KiB
rules/server-parallel-fetching.md1.5 KiB
rules/server-parallel-nested-fetching.md992 B
rules/server-serialization.md996 B

rules/server-hoist-static-io.md

title: Hoist Static I/O to Module Level impact: HIGH impactDescription: avoids repeated file/network I/O per request tags: server, io, performance, next.js, route-handlers, og-image

Hoist Static I/O to Module Level

Impact: HIGH (avoids repeated file/network I/O per request)

When loading static assets (fonts, logos, images, config files) in route handlers or server functions, hoist the I/O operation to module level. Module-level code runs once when the module is first imported, not on every request. This eliminates redundant file system reads or network fetches that would otherwise run on every invocation.

Incorrect (reads font file on every request):

// app/api/og/route.tsx
import { ImageResponse } from 'next/og'

export async function GET(request: Request) {
  // Runs on EVERY request - expensive!
  const fontData = await fetch(
    new URL('./fonts/Inter.ttf', import.meta.url)
  ).then(res => res.arrayBuffer())

  const logoData = await fetch(
    new URL('./images/logo.png', import.meta.url)
  ).then(res => res.arrayBuffer())

  return new ImageResponse(
    <div style={{ fontFamily: 'Inter' }}>
      <img src={logoData} />
      Hello World
    </div>,
    { fonts: [{ name: 'Inter', data: fontData }] }
  )
}

Correct (loads once at module initialization):

// app/api/og/route.tsx
import { ImageResponse } from 'next/og'

// Module-level: runs ONCE when module is first imported
const fontData = fetch(
  new URL('./fonts/Inter.ttf', import.meta.url)
).then(res => res.arrayBuffer())

const logoData = fetch(
  new URL('./images/logo.png', import.meta.url)
).then(res => res.arrayBuffer())

export async function GET(request: Request) {
  // Await the already-started promises
  const [font, logo] = await Promise.all([fontData, logoData])

  return new ImageResponse(
    <div style={{ fontFamily: 'Inter' }}>
      <img src={logo} />
      Hello World
    </div>,
    { fonts: [{ name: 'Inter', data: font }] }
  )
}

Correct (synchronous fs at module level):

// app/api/og/route.tsx
import { ImageResponse } from 'next/og'
import { readFileSync } from 'fs'
import { join } from 'path'

// Synchronous read at module level - blocks only during module init
const fontData = readFileSync(
  join(process.cwd(), 'public/fonts/Inter.ttf')
)

const logoData = readFileSync(
  join(process.cwd(), 'public/images/logo.png')
)

export async function GET(request: Request) {
  return new ImageResponse(
    <div style={{ fontFamily: 'Inter' }}>
      <img src={logoData} />
      Hello World
    </div>,
    { fonts: [{ name: 'Inter', data: fontData }] }
  )
}

Incorrect (reads config on every call):

import fs from 'node:fs/promises'

export async function processRequest(data: Data) {
  const config = JSON.parse(
    await fs.readFile('./config.json', 'utf-8')
  )
  const template = await fs.readFile('./template.html', 'utf-8')

  return render(template, data, config)
}

Correct (hoists config and template to module level):

import fs from 'node:fs/promises'

const configPromise = fs
  .readFile('./config.json', 'utf-8')
  .then(JSON.parse)
const templatePromise = fs.readFile('./template.html', 'utf-8')

export async function processRequest(data: Data) {
  const [config, template] = await Promise.all([
    configPromise,
    templatePromise,
  ])

  return render(template, data, config)
}

When to use this pattern:

Loading fonts for OG image generation
Loading static logos, icons, or watermarks
Reading configuration files that don't change at runtime
Loading email templates or other static templates
Any static asset that's the same across all requests

When not to use this pattern:

Assets that vary per request or user
Files that may change during runtime (use caching with TTL instead)
Large files that would consume too much memory if kept loaded
Sensitive data that shouldn't persist in memory

With Vercel's Fluid Compute, module-level caching is especially effective because multiple concurrent requests share the same function instance. The static assets stay loaded in memory across requests without cold start penalties.

In traditional serverless, each cold start re-executes module-level code, but subsequent warm invocations reuse the loaded assets until the instance is recycled.

Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Security

No issues found by our static scan· No issues found

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

Attribution and licence

Created by

vercel

Publisher

Vercel (Official)

Source

vercel-labs/agent-skills · skills/react-best-practices · commit 1a2c79d

Licence

MIT License (redistribution allowed)

ATTRIBUTION.md (written by AutoGineer)

Synced

2026-11-09

AutoGineer is not affiliated with or endorsed by vercel or Vercel.

Download ZIP

The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download vercel-react-best-practices.zip

From the author

AutoGineer summary

What it does

When to use it

Advantages

Usage examples

Install

Documentation by vercel

Vercel React Best Practices

When to Apply

Rule Categories by Priority

Quick Reference

1. Eliminating Waterfalls (CRITICAL)

2. Bundle Size Optimization (CRITICAL)

3. Server-Side Performance (HIGH)

4. Client-Side Data Fetching (MEDIUM-HIGH)

5. Re-render Optimization (MEDIUM)

6. Rendering Performance (MEDIUM)

7. JavaScript Performance (LOW-MEDIUM)

8. Advanced Patterns (LOW)

How to Use

Full Compiled Document

Files

rules/server-hoist-static-io.md

title: Hoist Static I/O to Module Level impact: HIGH impactDescription: avoids repeated file/network I/O per request tags: server, io, performance, next.js, route-handlers, og-image

Hoist Static I/O to Module Level

Requirements and compatibility

Security

Attribution and licence

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