431 Request Header Fields Too Large

What it means

Usually caused by oversized cookies accumulating on a domain.

Common causes

• Too many or very large cookies.
• A long Referer or custom header.

How to fix it

1. Clear cookies for the site.
2. Reduce cookie size on the server side.

Example response

HTTP/1.1 431 Request Header Fields Too Large
Content-Type: text/plain; charset=utf-8

Worked example

A client sends a request the server cannot fulfill as submitted. Check the response body and request details, correct the input or permissions, and retry only after the relevant issue is resolved.

How to read this response

1. Find the status line in your browser's Network panel, API client, or server access log.
2. Read the response body and headers shown above; headers such as Location, Allow, Retry-After, and WWW-Authenticate explain the next step.
3. Use the code's class to orient your diagnosis: informational, successful, redirected, request-related, or server-side.

How to check a status code

Enter a URL in the HTTP Status Checker to see its status code, every redirect hop, and response time. For redirect-heavy pages, the Website Speed Test shows how much time redirects add.

Frequently asked questions

What it means: HTTP 431

431 Request Header Fields Too Large: The request headers are too large for the server.

Common causes: 431

Too many or very large cookies. A long Referer or custom header.

How to fix it: HTTP 431

Clear cookies for the site. Reduce cookie size on the server side.

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