Content-Type et l’en-tête Accept

A response is more than a body. HTTP headers describe that body, and two of them decide how JSON flows between client and server. 📨

The Content-Type header announces the format of the body you are sending. For JSON replies its value is application/json.

You rarely set this header by hand. When you call jsonify, Flask attaches application/json automatically, so clients always parse correctly.

A browser or library reads Content-Type to decide how to handle the body. Seeing application/json, it parses text into a usable object.

Return JSON text as plain text/html and clients may not parse it. The body looks right but the missing signal breaks automatic decoding.

The request can carry an Accept header that lists formats the client wants. It is a wish, telling your server which response type fits best.

Keep the pair straight: Content-Type describes the body in the current message, while Accept states what the client hopes to receive back.

You can inspect the request to honor what the caller wants. The request.accept_mimetypes proxy reveals the formats listed in that header.

Serving the format a client asked for is called content negotiation. An API can return JSON or HTML for the same route based on Accept.

Incoming requests also carry Content-Type. When a client sends application/json, Flask knows the body is JSON and request.get_json can parse it.

For most JSON APIs, jsonify handling Content-Type is all you need. Reach for Accept only when one route must serve multiple formats.

Tell apart the two headers that shape JSON exchange.

You learned that Content-Type labels the body and Accept asks for a format, and that jsonify sets application/json so JSON clients just work. 🎉