HTTP Status Codes

The target resource does not have a current representation that would be acceptable to the user agent, according to the proactive negotiation header fields received in the request, and the server is unwilling to supply a default representation. The server SHOULD generate a payload containing a list of available representation characteristics and corresponding resource identifiers from which the user or user agent can choose the one most appropriate. A user agent MAY automatically select the most appropriate choice from that list. However, this specification does not define any standard for such automatic selection. This response is sent when the web server, after performing server-driven content negotiation, doesn't find any content following the criteria given by the user agent. The resource identified by the request is only capable of generating response entities which have content characteristics not acceptable according to the accept headers sent in the reques

The request has more than one possible responses. User-agent or user should choose one of them. There is no standardized way to choose one of the responses. The target resource has more than one representation, each with its own more specific identifier, and information about the alternatives is being provided so that the user (or user agent) can select a preferred representation by redirecting its request to one or more of those identifiers. In other words, the server desires that the user agent engage in reactive negotiation to select the most appropriate representation(s) for its needs. If the server has a preferred choice, the server SHOULD generate a Location header field containing a preferred choice's URI reference. The user agent MAY use the Location field value for automatic redirection. For request methods other than HEAD, the server SHOULD generate a payload in the 300 response containing a list of representation metadata and URI reference(s) from w