Next.js 15 Optimization Skill
Objective
Optimize Next.js applications to achieve:
- Perfect Core Web Vitals scores (LCP < 2.5s, FID < 100ms, CLS < 0.1)
- Fast page load times and optimal rendering strategies
- Efficient data fetching and caching
- Production-ready build configuration
- SEO and accessibility excellence
When to Use This Skill
Auto-invoke when:
- Project uses Next.js (detected by
nextin dependencies) - User mentions "optimize", "performance", "slow", or "Core Web Vitals"
- Before production deployment
- After adding new features or pages
- User requests Next.js-specific improvements
Prerequisites Check
Tools: Read, Grep
-
Verify Next.js version:
# Read package.json # Check for "next": "^15.0.0" or higher -
Detect App Router (Next.js 13+):
- Check for
app/directory - Check for
layout.tsx,page.tsxfiles
- Check for
-
Detect Pages Router (Legacy):
- Check for
pages/directory - Suggest migration to App Router
- Check for
Optimization Categories
1. Rendering Strategy Optimization
Goal: Choose optimal rendering for each page/component
Tools: Read, Grep, Edit
1.1 Server Components (Default in App Router)
When to use:
- Data fetching from APIs/databases
- Heavy computation
- Access to backend resources
Pattern:
// app/dashboard/page.tsx
export default async function DashboardPage() {
const data = await fetchData(); // Runs on server
return <Dashboard data={data} />;
}
Check for violations:
# Search for "use client" in components that don't need it
grep -r "use client" app/ | grep -v "onClick\|useState\|useEffect"
1.2 Client Components
When to use:
- Interactive UI (onClick, forms)
- Browser APIs (window, localStorage)
- React hooks (useState, useEffect)
Pattern:
// app/components/Counter.tsx
'use client';
export default function Counter() {
const [count, setCount] = useState(0);
return <button onClick={() => setCount(count + 1)}>{count}</button>;
}
Optimization: Keep client components small and leaf nodes
1.3 Static Generation (SSG)
When to use:
- Content that rarely changes
- Marketing pages, blogs, documentation
Pattern:
export const revalidate = 3600; // Revalidate every hour
export default async function BlogPost({ params }) {
const post = await getPost(params.slug);
return <Article post={post} />;
}
1.4 Dynamic Rendering with ISR
When to use:
- Content that changes periodically
- E-commerce products, user profiles
Pattern:
export const revalidate = 60; // Revalidate every minute
export async function generateStaticParams() {
const products = await getProducts();
return products.map((p) => ({ slug: p.slug }));
}
2. Image Optimization
Goal: Optimize images for performance and Core Web Vitals
Tools: Grep, Read, Edit
2.1 Use Next.js Image Component
Find unoptimized images:
grep -rn "<img " app/ src/
Replace with:
import Image from 'next/image';
<Image
src="/hero.jpg"
alt="Hero image"
width={1200}
height={600}
priority // For above-the-fold images
placeholder="blur" // Optional blur-up effect
/>
2.2 Configure Image Domains
Read next.config.js:
module.exports = {
images: {
remotePatterns: [
{
protocol: 'https',
hostname: 'example.com',
},
],
formats: ['image/avif', 'image/webp'], // Modern formats
},
};
2.3 Lazy Loading Strategy
- priority: Above-the-fold images (LCP candidates)
- loading="lazy": Below-the-fold images (default)
3. Font Optimization
Goal: Eliminate FOUT/FOIT and improve font loading
Tools: Read, Edit
3.1 Use next/font
Pattern:
// app/layout.tsx
import { Inter } from 'next/font/google';
const inter = Inter({
subsets: ['latin'],
display: 'swap', // Prevent FOIT
variable: '--font-inter',
});
export default function RootLayout({ children }) {
return (
<html lang="en" className={inter.variable}>
<body>{children}</body>
</html>
);
}
3.2 Self-Hosted Fonts
import localFont from 'next/font/local';
const customFont = localFont({
src: './fonts/CustomFont.woff2',
display: 'swap',
variable: '--font-custom',
});
4. Data Fetching Optimization
Goal: Minimize waterfalls and optimize cache
Tools: Read, Grep, Edit
4.1 Parallel Data Fetching
Anti-pattern (Sequential):
const user = await getUser();
const posts = await getPosts(user.id); // Waits for user
Optimized (Parallel):
const [user, posts] = await Promise.all([
getUser(),
getPosts(),
]);
4.2 Streaming with Suspense
Pattern:
import { Suspense } from 'react';
export default function Page() {
return (
<>
<Header />
<Suspense fallback={<Skeleton />}>
<SlowComponent />
</Suspense>
<Footer />
</>
);
}
4.3 Cache Configuration
// Aggressive caching
fetch('https://api.example.com/data', {
next: { revalidate: 3600 }, // Cache for 1 hour
});
// No caching
fetch('https://api.example.com/data', {
cache: 'no-store', // Always fresh
});
// Opt out of caching
export const dynamic = 'force-dynamic';
5. Bundle Optimization
Goal: Reduce JavaScript bundle size
Tools: Bash, Read, Edit
5.1 Analyze Bundle
# Add to package.json scripts
npm run build
npx @next/bundle-analyzer
5.2 Dynamic Imports
Find large components:
find app -name "*.tsx" -exec wc -l {} \; | sort -rn | head -10
Split with dynamic imports:
import dynamic from 'next/dynamic';
const HeavyComponent = dynamic(() => import('./HeavyComponent'), {
loading: () => <Skeleton />,
ssr: false, // Skip SSR if not needed
});
5.3 Tree Shaking
Check for barrel exports:
grep -rn "export \* from" app/
Replace with specific imports:
// Anti-pattern
import { Button, Card, Modal } from '@/components';
// Optimized
import { Button } from '@/components/Button';
6. Metadata & SEO
Goal: Perfect SEO and social sharing
Tools: Read, Edit
6.1 Static Metadata
// app/layout.tsx
export const metadata = {
title: {
default: 'My App',
template: '%s | My App',
},
description: 'Description for SEO',
openGraph: {
title: 'My App',
description: 'Description for social sharing',
images: ['/og-image.jpg'],
},
twitter: {
card: 'summary_large_image',
},
};
6.2 Dynamic Metadata
export async function generateMetadata({ params }) {
const post = await getPost(params.slug);
return {
title: post.title,
description: post.excerpt,
openGraph: {
images: [post.ogImage],
},
};
}
7. Production Configuration
Goal: Optimize next.config.js for production
Tools: Read, Edit
7.1 Essential Config
// next.config.js
module.exports = {
reactStrictMode: true,
poweredByHeader: false, // Security
compress: true, // Gzip compression
// Compiler optimizations
compiler: {
removeConsole: process.env.NODE_ENV === 'production',
},
// Image optimization
images: {
formats: ['image/avif', 'image/webp'],
deviceSizes: [640, 750, 828, 1080, 1200, 1920],
},
// React Compiler (Next.js 15)
experimental: {
reactCompiler: true,
},
};
7.2 Turbopack (Development)
// package.json
{
"scripts": {
"dev": "next dev --turbo"
}
}
8. Core Web Vitals Optimization
Goal: Achieve perfect Lighthouse scores
Tools: Bash, Grep, Edit
8.1 LCP (Largest Contentful Paint) < 2.5s
Optimize:
- Use
priorityon hero images - Preload critical resources
- Server-side render ab