506 Variant Also Negotiates
HTTP response status code 506 Variant Also Negotiates is a server error message that occurs during Transparent Content Negotiation. It is an internal misconfiguration error that occurs when a specified endpoint is not a valid HTTP endpoint.
When the 506 Variant Also Negotiates status code is received, it happens during Transparent Content Negotiation, where the protocol facilitates the client receiving the best variant of the target resource if multiple variants are available.
Variants are different versions of the subject resource. For example, if a resource is available in several different languages then it may have a variant for each one. Transparent Content Negotiation will automatically allow the client to receive the best variant when a GET or HEAD HTTP request is made.
In March 1998, this protocol was described as experimental and has not been officially adopted as a standard.
Apache HttpComponents Core
The 506 Variant Also Negotiates status code is a server error that occurs during Transparent Content Negotiation, although this HTTP protocol is experimental and unlikely to be encountered.