SKILL.md

name: nextjs-performance description: Next.js performance optimizations including next/image, next/font, dynamic imports, caching strategies, and bundle optimization. Use when optimizing Next.js apps for speed or Core Web Vitals.

Next.js Performance

Expert guidance for optimizing Next.js applications.

Quick Reference

Concern	Solution	Impact
Images	next/image with sizing	CLS prevention, auto-optimization
Fonts	next/font	No layout shift, self-hosted
Heavy components	next/dynamic	Reduced initial bundle
Data caching	fetch options (revalidate)	Reduced server load
Client navigation	Link component	Instant transitions
Bundle size	Tree shaking, no unused deps	Faster JS loading

What Do You Need?

Image optimization - next/image usage, sizing, formats
Font loading - next/font, preloading
Code splitting - Dynamic imports, route splitting
Caching - ISR, revalidation, cache strategies
Navigation - Link usage, prefetching

Specify a number or describe your performance concern.

Routing

Response	Reference to Read
1, "image", "img", "optimization", "cls"	images.md
2, "font", "layout shift", "typography"	fonts.md
3, "dynamic", "import", "lazy", "split"	code-splitting.md
4, "cache", "revalidate", "isr", "fetch"	caching.md
5, "navigation", "link", "prefetch"	navigation.md

Essential Principles

Optimize images: Use next/image with width/height for all images. Prevents CLS and enables automatic optimization.

Self-host fonts: Use next/font to eliminate requests to external font services and prevent layout shift.

Dynamic import heavy code: Use next/dynamic for components that are heavy or not immediately visible.

Client-side navigation: Use Link component for all internal links. Enables instant page transitions.

Cache strategically: Use appropriate fetch caching (force-cache, no-store, revalidate) based on data freshness needs.

Common Performance Issues

Issue	Severity	Impact	Fix
Using `<img>` instead of next/image	High	CLS, no optimization	Use next/image
External fonts	Medium	Layout shift, extra request	Use next/font
Large initial bundle	High	Slow initial load	Dynamic imports
No caching on static data	Medium	Unnecessary server load	Add revalidate
Using `<a>` instead of Link	High	Full page reload	Use Link
No priority hints	Low	Delayed LCP	Use priority prop

Code Patterns

Images

// Good: next/image with sizing
import Image from 'next/image'

<Image
  src="/avatar.jpg"
  width={100}
  height={100}
  alt="Avatar"
  priority // For above-fold images
/>

Fonts

// Good: next/font
import { Inter } from 'next/font/google'

const inter = Inter({ subsets: ['latin'] })

export default function RootLayout({ children }: { children: ReactNode }) {
  return <html className={inter.className}>{children}</html>
}

Dynamic Imports

// Good: Dynamic import for heavy component
import dynamic from 'next/dynamic'

const HeavyChart = dynamic(() => import('./HeavyChart'), {
  loading: () => <div>Loading...</div>,
  ssr: false, // If client-only
})

Caching

// Good: Appropriate caching
export const revalidate = 3600 // Revalidate every hour

async function getData() {
  const res = await fetch('https://api.example.com/data', {
    next: { revalidate: 3600 } // or { revalidate: 0 } for no cache
  })
  return res.json()
}

Reference Index

File	Topics
images.md	next/image, sizing, priority, formats
fonts.md	next/font, Google fonts, local fonts
code-splitting.md	Dynamic imports, route splitting
caching.md	fetch options, ISR, revalidatePath
navigation.md	Link component, prefetching, scroll

Success Criteria

Performance is good when:

All images use next/image with proper sizing
Fonts loaded with next/font (no layout shift)
Heavy components dynamically imported
Static data cached appropriately (revalidate set)
All internal links use Link component
LCP < 2.5s, FID < 100ms, CLS < 0.1

Score

Total Score

65/100

Based on repository quality metrics

✓SKILL.md

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+10

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+10

○人気

GitHub Stars 100以上

0/15

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3ヶ月以内に更新がある

0/10

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10回以上フォークされている

0/5

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+5

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0/5

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