HTTP status code

An HTTP status code is a three-digit code in an HTTP response describing the outcome or progress of handling an HTTP request. Its first digit identifies a broad class: informational 1xx, successful 2xx, redirection 3xx, client-error 4xx or server-error 5xx. The particular code and request method refine the meaning.^[ref]

For an invented /color resource, a PUT can store blue and return 204 to indicate successful fulfillment without response content. A later GET can return 200 with the text blue. A HEAD response can also have status 200 while carrying no response content. Thus a successful code does not by itself determine whether there is a body to read.^[ref]

In HTTP/1.1, a status line might be written HTTP/1.1 200 OK. The numerical code supplies the standardized status; the accompanying reason phrase is optional and is not the authority for interpretation. Changing the descriptive phrase does not redefine code 200.^[ref]

An HTTP status code describes this exchange rather than proving that every application-level goal succeeded. A request can be transferred correctly and still receive an error status. Conversely, receiving 200 does not establish that an application-specific calculation inside the returned content is correct. Interpret status, HTTP header fields, content and the application's contract together.