HTTP Error 431 Fix: How to Resolve “Request Header Fields Too Large” Issue

HTTP Error 431, also known as “Request Header Fields Too Large”, occurs when the server refuses to process a request because the header fields are too large. This can happen if a single header field or the total size of all header fields exceeds the limit set by the server.

Common Causes of HTTP Error 431

Several factors can lead to this error, including:

1. Excessive Cookies: Too many cookies stored in the browser can increase the size of the request headers, leading to this error.
2. Long URLs in Referer Header: If the request contains an extremely long Referer URL, it can contribute to oversized headers.
3. Excessive Custom Headers: Web applications or extensions may add too many custom headers, making the request unprocessable by the server.
4. Server-Side Limitations: Some web servers have strict limits on request header sizes. If these limits are too low, even normal requests might trigger the error.
5. Misconfigured Proxy or API Calls: Using incorrect proxy configurations in front-end applications (such as React with Node.js) can lead to an internal loop, inflating the request header size.

How to Fix HTTP Error 431

For Regular Users (Browser-Side Fixes)

1. Clear Browser Cookies: Since cookies contribute to large headers, clearing them can help resolve the issue.

• In Chrome: Go to Settings > Privacy and security > Clear browsing data and select Cookies and other site data.
• In Firefox: Go to Settings > Privacy & Security > Cookies and Site Data > Clear Data.

2. Use Incognito Mode: Open the website in an Incognito/Private window to check if cookies are the problem.

3. Reduce the URL Length: If the error occurs due to an excessively long URL, try shortening it before making the request.

4. Disable Browser Extensions: Some extensions may inject additional headers into requests. Try disabling extensions and reloading the page.

For Developers and Website Administrators (Server-Side Fixes)

1. Increase Header Size Limits: If you have control over the web server, increase the allowable header size.

• In Apache, modify the LimitRequestFieldSize directive in the server configuration.
• In NGINX, increase the large_client_header_buffers setting.

2. Optimize Cookies Usage: Minimize the number of cookies sent in each request. Store only necessary data.

3. Restrict Custom Headers: Avoid sending excessive or unnecessary headers from the client-side.

4. Check API Calls in React & Node.js Applications:

Issue: Many developers encounter this error when using a React front-end with a Node.js back-end. If an API request works in Postman but fails in a browser, it’s likely due to excessive cookies or an incorrect proxy setup.

Debugging Steps:

• Log request headers on the server-side: console.log(req.headers);
• Compare Postman requests with browser requests to identify differences.
• Ensure that the proxy in package.json matches the server’s port.
• Consider removing the proxy from package.json and explicitly defining the API URL in Axios calls.

5. Check for Infinite Loops in Proxy Configuration:

• Some developers mistakenly set the proxy destination to the same port as their React app, creating an internal forwarding loop.
• Ensure that the proxy points to the correct back-end server, not the same port as the front-end.

6. Use Server Logs for Debugging: Check server logs to determine which specific header is causing the issue and adjust configurations accordingly.

Example Error & Fix

Example: React & Node.js (MERN Stack) Issue

A developer building a MERN stack application encountered this error:

Failed to load resource: the server responded with a status of 431 (Request Header Fields Too Large)

• The API was working fine in Postman but not in the browser.
• The issue was traced to excessive cookies stored in the browser.
• Solution: Clearing cookies fixed the issue.

Final Thoughts

HTTP Error 431 is a client-side issue that can often be resolved by clearing cookies, reducing URL lengths, or managing browser extensions. If you are a developer or website owner, reviewing server configurations and optimizing headers can prevent this error from occurring frequently.

By applying the fixes mentioned above, you can resolve this issue and ensure a smooth browsing experience for your users.

Have you encountered HTTP Error 431? Let us know how you fixed it in the comments!