Content · Request & Response

Content-Type

Declares the media type of the body.

What is Content-Type?

Content-Type tells the receiver how to interpret the bytes in the message body — as JSON, HTML, an image, a video, and so on. Almost every request with a body and every response with content must set it correctly, or the client / browser will misinterpret the payload.

Typical usage

Always set on responses with a body; also required on POST / PUT / PATCH requests that carry a body.

Examples

JSON body

Content-Type: application/json

HTML page (with charset)

Content-Type: text/html; charset=utf-8

Form with file upload

Content-Type: multipart/form-data; boundary=----WebKitFormBoundary...

Common gotchas

Serving a script or stylesheet with the wrong Content-Type causes the browser to reject it silently. Always match the actual bytes — a .css file must be sent as text/css.

Specification

RFC 9110 §8.3

Related headers

Which media types the client can process.

Content-Length

The size of the body in bytes.

Content-Encoding

How the body has been transparently encoded (usually compressed).

Content-Disposition

Controls whether a resource is displayed inline or triggered as a download.