Fixing Hydration Errors in Next.js

2026-05-22

Fixing Hydration Errors in Next.js 1232

Introduction

Hydration mismatch errors are common in SSR applications built with Next.js.

In this article, we will understand:

  • why it happens
  • common causes
  • proper fixes
  • best practices

Problem

You may encounter this error:

A tree hydrated but some attributes of the server rendered HTML didn't match the client properties

Why It Happens

Next.js first renders HTML on the server.

If the client-side render produces different HTML during hydration, React throws a mismatch warning.

Common causes:

  • browser extensions
  • Date.now()
  • Math.random()
  • window checks
  • SSR/client mismatch

Solution

Add suppressHydrationWarning

<body suppressHydrationWarning>

Avoid Dynamic Values During SSR

Bad:

const id = Math.random();

Good:

useEffect(() => {
  setId(Math.random());
}, []);

Best Practices

  • Keep server/client rendering consistent
  • Avoid browser-only APIs during SSR
  • Use client components carefully
  • Test production builds locally

Conclusion

Hydration errors are common in SSR applications. Understanding how React hydration works helps prevent these issues effectively.