application/cbor

JSON's data model in binary, engineered for machines that can't afford a parser: CBOR targets tiny code size and messages that need no version negotiation, which is why it underpins WebAuthn attestations, COSE signatures, and CoAP on constrained devices. RFC 8949 (2020) promoted it to Internet Standard, obsoleting the original RFC 7049 from 2013. There is no mandatory magic number — the self-describing tag 55799 (bytes d9 d9 f7) exists precisely to give a CBOR file a recognizable head, but it is optional and most encoders skip it, so sniffing CBOR is guesswork.

Defined by RFC 8949 · IANA registration. Registry facts from the IANA media-types registry via mime-db.