Next.js Performance Analytics — Client & Server Usage Guide

Overview

Performance in a Next.js application depends on multiple factors such as JavaScript bundle size, server component efficiency, navigation speed, image optimization, script loading, and key Web Vitals metrics. Proper monitoring and optimization in these areas ensures your app is fast, responsive, and SEO-friendly.

Client-Side Performance Checks

On the client side, performance issues often arise from heavy JavaScript bundles, inefficient client components, and unoptimized resource loading.

1. JavaScript Bundle Size

Large bundles slow page load and interactivity.

npm install @next/bundle-analyzer

next.config.js:

const withBundleAnalyzer = require('@next/bundle-analyzer')({
  enabled: process.env.ANALYZE === 'true',
});
 
module.exports = withBundleAnalyzer({});

ANALYZE=true npm run build

Checks:

• Look for large libraries (MUI, Lodash, Chart.js)
• Repeated code across chunks
• Unoptimized imports

Fixes:

• Convert components to Server Components where possible
• Lazy-load heavy components with dynamic()
• Tree-shake libraries
• Remove unused dependencies

2. Navigation Lag

Lag happens when route changes trigger heavy re-renders or unnecessary fetches.

Checks:

• Are data fetching calls repeated on every route change?
• Are layouts heavy or contain many client components?

Fixes:

• Use React Suspense with loading.js
• Cache requests (fetch(..., { cache: "force-cache" }))
• Keep layouts lightweight
• Move heavy logic to server components

3. Images & Scripts

Images (next/image)

Optimized images improve LCP and reduce CLS.

Best Practices:

• Set width and height to prevent layout shifts
• Use priority for hero images
• Use placeholder="blur" for smoother loading
• Include alt for SEO

Scripts (next/script)

Strategy Options:

Fixes:

• Avoid blocking hydration
• Load non-critical scripts lazily
• Minimize main-thread work

Server-Side Performance (SSR/SSG)

Server-side performance affects TTFB, LCP, and overall page load.

1. Server Components

Checks:

• Are heavy computations inside server components?
• Are large datasets fetched without caching?

Fixes:

• Cache queries (revalidate, Redis, or CDN)
• Split heavy logic into smaller components
• Paginate large datasets
• Use server actions for mutations

2. Prefetching Data

Prefetch data during SSR to reduce client-side fetching and improve UX.

import { QueryClient, dehydrate } from '@tanstack/react-query'
 
const queryClient = new QueryClient()
 
await queryClient.prefetchQuery({
  queryKey: ['users'],
  queryFn: () => fetch('/api/users').then(res => res.json())
})
 
const dehydratedState = dehydrate(queryClient)

• Use HydrationBoundary to pass the prefetched data to the client
• Prevents unnecessary network requests after initial render

Core Performance Metrics (Web Vitals)

Next.js provides the useReportWebVitals hook to monitor performance:

import { useReportWebVitals } from 'next/web-vitals'
 
useReportWebVitals(metric => console.log(metric))

Or you can use Lighthouse  extension to look further into this performance metrics.

Metrics Overview

Recommended Docs

For the most up-to-date and detailed information, please refer to the official documentation:

• Web Vitals
• Next.js Analytics
• Next.js Performance

Summary Checklist