The request's HTTP headers are too long.


  1. The server is unwilling to process the request because its header fields are too large.
  2. The request may be resubmitted after reducing the size of the request header fields.
  3. It can be used both when the set of request header fields in total is too large, and when a single header field is at fault.
  4. In the latter case, the response representation should specify which header field was too large.


HTTP/1.1 431 Request Header Fields Too Large
Content-Type: text/html
    <title>Request Header Fields Too Large</title>
    <h1>Request Header Fields Too Large</h1>
    <p>The "Example" header was too large.</p>

Responses with the 431 status code must not be stored by a cache.


431 can be used when the total size of request headers is too large, or when a single header field is too large. To help those running into this error, indicate which of the two is the problem in the response body — ideally, also include which headers are too large. This lets users attempt to fix the problem, such as by clearing their cookies.

Further Reading


431 Request Header Fields Too Large | The HTTP Working Group

431 Request Header Fields Too Large

MDN web docs