Status code 431

This week was the first time I encountered status code 431 and did some research into it as we were seeing it happening in a few places. I thought I'd share my findings so that if you're encountering this issue, you've got a good starting point.

What does it mean?

According to the MDN website:

The HTTP 431 Request Header Fields Too Large response status code indicates that the server refuses to process the request because the request's HTTP headers are too long. The request may be resubmitted after reducing the size of the request headers.

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.