414 Request-URI Too Long - Client Error Response Status Code

Official Definition

The 414 (URI Too Long) status code indicates that the server is refusing to service the request because the request-target (Section 5.3 of [RFC7230]) is longer than the server is willing to interpret. This rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long query information, when the client has descended into a "black hole" of redirection (e.g., a redirected URI prefix that points to a suffix of itself) or when the server is under attack by a client attempting to exploit potential security holes.

A 414 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls.

Source: RFC 7231 Section 6.5.11