HTTP 431 — Request Header Fields Too Large
The server is unwilling to process the request because either an individual header field, or all the header fields collectively, are too large
When to use it
Use status 431 when this is the correct HTTP response semantic: The server is unwilling to process the request because either an individual header field, or all the header fields collectively, are too large
Request and response example
GET /protected-resource HTTP/1.1
Host: api.example.com
HTTP/1.1 431 Request Header Fields Too Large
Content-Type: application/json
{"error":"Request cannot be completed"}