HTTP 431 Request Header Fields Too Large — What It Means & How to Fix It

The HTTP 431 Request Header Fields Too Large status code indicates the server refuses the request because the HTTP headers are too large. This guide covers everything you need to know about this topic, including common causes, step-by-step solutions, and answers to frequently asked questions.

Here are the key things to understand: This status code is defined in RFC 6585.. It can be triggered by a single header that is too large or by the total size of all headers.. Common when cookies grow too large or too many cookies are set.. The client should reduce the size of request headers and retry.. Understanding these fundamentals will help you diagnose and resolve this issue more effectively.

The most common reasons this occurs include: Too many cookies are being sent with the request.. Individual cookies have grown very large.. Custom headers contain excessive data.. Authentication tokens in headers are unusually large.. Identifying the root cause is the first step toward finding the right solution.

To resolve this, follow these recommended steps: Clear cookies for the affected domain and retry.. Review and reduce the number and size of cookies.. Move large data from headers to the request body.. If the problem is a large authentication token, investigate why it is so large.. Increase server header size limits if the headers are legitimately needed.. If these steps do not resolve the issue, consider consulting additional resources or a qualified professional.

This article is part of our HTTP Status Codes collection on Error Codes Wiki. We provide comprehensive, up-to-date information to help you find solutions quickly.