Fix Next.js Hydration Error: Expected server HTML to contain a matching tag (2025 Guide)

Posted on: April 19, 2025

Encountered a "Hydration Error: Expected server HTML to contain a matching tag" in Next.js? This error occurs when the server-rendered HTML doesn’t match the client-rendered HTML during React’s hydration process. Let’s fix it fast in this 2025 guide!

What Causes "Hydration Error: Expected server HTML to contain a matching tag"?

This error happens due to mismatches between server-side rendering (SSR) and client-side rendering in Next.js. Common causes include:

• Client-Side Logic in SSR: Using browser-specific logic (like `window` or `useEffect`) during server rendering.
• Conditional Rendering: Rendering different content on the server vs. client based on conditions.
• Dynamic Updates: State changes on the client that don’t match the initial server render.

Check this demo (open console with F12):

Here, the component renders differently on the server and client, triggering the hydration error.

How to Fix It: 3 Solutions

Let’s resolve this error with practical steps:

(Diagram: Developer renders component, gets error, adjusts logic, runs successfully.)

Solution 1: Move Client-Side Logic to useEffect

Ensure client-specific logic runs only on the client using `useEffect`:

import { useState, useEffect } from 'react';

function MyComponent() {
  const [isClient, setIsClient] = useState(false);

  useEffect(() => {
    setIsClient(true);
  }, []);

  return 
{isClient ? 'Client Rendered' : 'Server Rendered'}
;
}

export default MyComponent;

Using `useEffect` ensures the state change happens only on the client, avoiding mismatches.

Solution 2: Ensure Consistent Rendering

Make sure the server and client render the same content by avoiding browser-specific checks:

import { useState, useEffect } from 'react';

function MyComponent() {
  const [isMounted, setIsMounted] = useState(false);

  useEffect(() => {
    setIsMounted(true);
  }, []);

  return 
{isMounted ? 'Client' : 'Server'}
;
}

export default MyComponent;

Avoid direct `window` checks and use state to manage rendering differences.

Solution 3: Suppress Hydration Warning (If Necessary)

If the mismatch is intentional and safe, suppress the warning:

function MyComponent() {
  return (
    

      {/* Content that might mismatch */}
      This content may differ between server and client.
    
  );
}

export default MyComponent;

Use `suppressHydrationWarning` cautiously, only when you’re sure the mismatch won’t break functionality.

Quick Checklist

• Client-side logic in SSR? (Move to `useEffect`)
• Inconsistent rendering? (Ensure server and client match)
• Intentional mismatch? (Use `suppressHydrationWarning`)

Conclusion

The "Hydration Error: Expected server HTML to contain a matching tag" in Next.js can be resolved by ensuring consistent rendering between server and client. With these 2025 solutions, your app will run smoothly. Got another Next.js error? Let us know in the comments!