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Vercel React Best Practices

JetBrainsOfficialCreated by VercelDistributed by JetBrains

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  • Software development
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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

Vercel React Best Practices provides a structured set of 64 rules designed to guide developers in writing and refactoring React and Next.js code. The guidelines are organized into eight categories ranging from eliminating request waterfalls and optimizing bundle sizes to managing re-renders and server-side performance. Each rule is categorized by priority to help developers focus on high-impact improvements for their applications.

What it does

  • Provides 64 specific rules for React and Next.js optimization
  • Categorizes rules by priority and impact level
  • Offers guidance on eliminating request waterfalls
  • Includes patterns for bundle size and server-side performance
  • Details techniques for managing client-side data fetching and re-renders
  • Supplies reference material for advanced React patterns

When to use it

  • When writing new React components or Next.js pages
  • During the implementation of client or server-side data fetching
  • When reviewing code for performance patterns
  • When refactoring existing React or Next.js codebases
  • When aiming to reduce bundle size or improve load times

Advantages

  • Organized by priority to address critical issues first
  • Covers a wide range of performance-related topics
  • Maintained by Vercel for relevance to the Next.js ecosystem
  • Provides clear prefixes for identifying rule categories

Usage examples

“How can I improve my data fetching in a Next.js page to avoid waterfalls?”
The agent will reference rules like async-parallel and async-defer-await to suggest using Promise.all or deferring await statements.
“What is the best way to handle heavy components in my React app?”
The agent will suggest using bundle-dynamic-imports to implement next/dynamic for better bundle management.

Install

  1. Download the skill as a ZIP:

    https://mp-staging.autogineer.com/agent-skills/jetbrains/vercel-react-best-practices/download

  2. 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 64 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

PriorityCategoryImpactPrefix
1Eliminating WaterfallsCRITICALasync-
2Bundle Size OptimizationCRITICALbundle-
3Server-Side PerformanceHIGHserver-
4Client-Side Data FetchingMEDIUM-HIGHclient-
5Re-render OptimizationMEDIUMrerender-
6Rendering PerformanceMEDIUMrendering-
7JavaScript PerformanceLOW-MEDIUMjs-
8Advanced PatternsLOWadvanced-

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-hoist-static-io - Hoist static I/O (fonts, logos) to module level

  • 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-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

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

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

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 }] }
  )
}

Alternative: synchronous file reads with Node.js fs

// 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 }] }
  )
}

General Node.js example: loading config or templates

// Incorrect: reads config on every call
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: loads once at module level
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.

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Attribution and licence

Created by
Vercel
Publisher
JetBrains (Official)
Distributed by
JetBrains
Source
JetBrains/skills · react-best-practices · commit 3f53782
Licence
MIT License (redistribution allowed)
  • ATTRIBUTION.md (written by AutoGineer)
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