4xx Client error
431 Request Header Fields Too Large
The request headers are too large.
Almost always caused by too many or too large cookies, or a very long Authorization / Referer header.
Common causes and fixes
- Clear the site’s cookies; avoid storing large data in cookies.
- Raise the server limit if needed (e.g. nginx
large_client_header_buffers, Node--max-http-header-size).
Example response
HTTP/1.1 431 Request Header Fields Too Large
Date: Thu, 22 Oct 2026 08:00:00 GMT Check a URL’s status with curl -I https://example.com, which prints the status line and headers.