Fix "Hydration failed because the initial UI does not match" in Next.js

Quick answer: Server HTML differs from what React renders in the browser.

Hydration failed because the initial UI does not match what was rendered on the server

Why it happens

Server HTML differs from what React renders in the browser. It's one of the most common errors in AI-generated projects because AI tools often add imports or packages without updating your install or config.

How to fix it

1. Look for Date.now(), Math.random(), or window use during render.
2. Move browser-only code into useEffect.
3. Fix invalid nesting like <div> inside <p>.
4. Disable SSR for that component with dynamic(..., { ssr:false }) if needed.

Prompt to paste into your AI tool

I got this error: "Hydration failed because the initial UI does not match what was rendered on the server". Before changing any code, explain the root cause in 2 sentences, list the files involved, then propose the smallest fix.

Still stuck? Paste your exact error into the free Error Fixer.