431 Request Header Fields Too Large

The request headers are too large, all together or one alone. Often an oversized cookie.

What to do

The request headers are too large, most often because of a pile of cookies. Clearing the site's cookies usually fixes it. Node.js sends it past the limit set by --max-http-header-size.

Class
4xx Client Error. The request has a fault, or cannot be met as sent.
Registered
Yes, in the IANA HTTP status code registry.
Cacheable by default
No. A cache stores it only when Cache-Control or Expires says to.
References
RFC 6585 ยง5 · MDN

Every 4xx code

All HTTP status codes, in one table