application/json

The lingua franca of APIs: JavaScript's object syntax, frozen into a data format. Send it for anything structured that isn't a file — and never with a charset parameter, because JSON is defined as UTF-8 on the wire and the parameter has no effect. The classic mistake is text/json, which no standard defines: parsers tolerate it, content negotiation doesn't.

.map is the sourcemap convention, also served as JSON.

Defined by RFC 8259 · IANA registration. Registry facts from the IANA media-types registry via mime-db.