Network Working Group R. Fielding Request for Comments: 2616 ...

public why the request has not been fulfilled, it SHOULD describe thereason for the refusal in the entity. If the server does not wish tomake this information available to the client, the status code 404(Not Found) can be used instead.10.4.5 404 Not FoundThe server has not found anything matching the Request-URI. Noindication is given of whether the condition is temporary orpermanent. The 410 (Gone) status code SHOULD be used if the serverknows, through some internally configurable mechanism, that an oldresource is permanently unavailable and has no forwarding address.This status code is commonly used when the server does not wish toreveal exactly why the request has been refused, or when no otherresponse is applicable.10.4.6 405 Method Not AllowedThe method specified in the Request-Line is not allowed for theresource identified by the Request-URI. The response MUST include anAllow header containing a list of valid methods for the requestedresource.Fielding, et al. Standards Track [Page 66]RFC 2616 HTTP/1.1 June 199910.4.7 406 Not AcceptableThe resource identified by the request is only capable of generatingresponse entities which have content characteristics not acceptableaccording to the accept headers sent in the request.Unless it was a HEAD request, the response SHOULD include an entitycontaining a list of available entity characteristics and location(s)from which the user or user agent can choose the one mostappropriate. The entity format is specified by the media type givenin the Content-Type header field. Depending upon the format and thecapabilities of the user agent, selection of the most appropriatechoice MAY be performed automatically. However, this specificationdoes not define any standard for such automatic selection.Note: HTTP/1.1 servers are allowed to return responses which arenot acceptable according to the accept headers sent in therequest. In some cases, this may even be preferable to sending a406 response. User agents are encouraged to inspect the headers ofan incoming response to determine if it is acceptable.