Not-found page handling in NextJS - Performance & Optimization

Performance: Not-found page handling

MEDIUM IMPACT

This affects the page load speed and user experience when a user navigates to a non-existent route.

Handling a user visiting a non-existent page

NextJS

import { notFound } from 'next/navigation';

export default function Page() {
  // Next.js built-in to trigger 404
  notFound();
  return null;
}

Using Next.js built-in notFound() triggers server-side 404 response and faster error page display.

📈 Performance GainImproves LCP by serving 404 quickly; reduces unnecessary client JS; better SEO

Handling a user visiting a non-existent page

NextJS

export default function Page() {
  return <div>Page not found</div>;
}

// No special 404 handling, no status code set

This does not set the HTTP 404 status code, causing search engines and browsers to treat it as a normal page, and may delay showing the user the correct error.

📉 Performance CostBlocks rendering until client-side JS loads; no server-side 404 status means slower LCP and SEO issues

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Client-side 404 rendering without status	Moderate (full page DOM)	Multiple (full layout)	High (full paint)	[X] Bad
Server-side 404 with notFound()	Minimal (error page DOM)	Single reflow	Low (simple paint)	[OK] Good

Rendering Pipeline

When a not-found page is handled properly, the server sends a 404 status early, skipping unnecessary data fetching and rendering, so the browser can quickly paint the error page.

→Server Response

→Style Calculation

→Layout

→Paint

⚠️ BottleneckServer Response when notFound is not used, causing delayed error page delivery

Core Web Vital Affected

LCP

This affects the page load speed and user experience when a user navigates to a non-existent route.

Optimization Tips

1Always use Next.js notFound() to trigger server-side 404 status.

2Avoid rendering 404 messages only on the client side without status code.

3Keep the not-found page simple to reduce paint time and improve LCP.

Performance Quiz - 3 Questions

What is the main performance benefit of using Next.js's notFound() for not-found page handling?

A It triggers a server-side 404 status and faster error page rendering

B It loads extra JavaScript for better animations

C It delays the error page to fetch more data

D It disables caching for the page

DevTools: Network

How to check: Open DevTools, go to Network tab, reload a non-existent page, and check the status code of the response.

What to look for: A 404 status code confirms proper not-found handling; absence means bad pattern.