Fix Next.js hydration mismatch errors
Hydration errors occur when the server-rendered HTML doesn't match what React expects on the client. This is one of the most common Next.js issues, often caused by browser extensions, invalid HTML nesting, or code that behaves differently on server vs client.
Error messages you might see
Hydration failed because the initial UI does not match what was rendered on the server.There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.Why this happens in AI-generated code
Server/client rendering mismatch
AI-generated code often uses Date.now(), Math.random(), or window-dependent values directly in component render, producing different output on server vs client.
Invalid HTML nesting
AI tools frequently nest block elements inside inline elements (e.g., a <div> inside a <p>), which browsers correct automatically, causing a mismatch.
Browser extensions injecting DOM nodes
Extensions like Grammarly or password managers inject extra elements into the DOM that weren't present during server rendering, triggering hydration failures.
How to fix it
Use useEffect for client-only values
Move any code that depends on browser APIs or produces non-deterministic output into a useEffect hook so it only runs after hydration completes.
Add suppressHydrationWarning or use dynamic imports
For intentionally dynamic content, add suppressHydrationWarning to the element or use next/dynamic with ssr: false to skip server rendering entirely.
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Frequently asked questions
Why does my Next.js app work in development but show hydration errors in production?
Development mode is more lenient with hydration mismatches. Production builds use stricter checks and will throw errors that dev mode silently patches over.
Can hydration errors cause SEO problems?
Yes. When hydration fails, React may discard the server-rendered HTML and re-render entirely on the client, which means search engine crawlers may see different content than users.
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