Content-Type field

Meaning

Content-Type identifies the media type of the representation associated with the message. The media type tells a recipient what the data format is and how it is intended to be processed after any Content-Encoding is decoded.

Content-Type: application/json; charset=utf-8

Expected result: the recipient interprets the associated representation as JSON. The parameter is part of the media type; it is not a separate HTTP field.

Requests and responses

On a request with content, Content-Type describes the submitted representation. It does not state which response formats the client accepts; that is the role of fields such as Accept. On a response, it describes the selected representation returned by the server.

A sender that knows the media type should send the field. Missing or incorrect metadata can make a recipient reject the content, treat it as generic binary data, or apply format-sniffing behavior that varies by implementation.

Parameters and content coding

Media-type parameters refine the type. For example, a charset parameter can identify a character encoding when the media type defines that parameter. Content-Encoding: gzip is different: it describes an additional coding applied to the typed representation.

Common mistakes

• Do not use a filename extension as a substitute for the field.
• Do not send JSON as text/plain merely to avoid a browser preflight.
• Do not confuse Content-Type with Accept or Content-Encoding.
• Validate that the body actually conforms to the declared media type.