CBOR: It’s like JSON but fast and small but also an official IETF standard.
CBOR is MessagePack. The story is that Carsten Bormann wanted to create an IETF standardized MP version, the creators asked him not to (after he acted in pretty bad faith), he forked off a version, added some very ill-advised tweaks, named it after himself, and submitted it anyway.
I wrote this up years ago (https://news.ycombinator.com/item?id=14072598), and since then the only thing they've addressed is undefined behavior when a decoder encounters an unknown simple value.
https://www.w3.org/TR/webauthn-2/#sctn-conforming-all-classe...
Reading through this, it looks like they toss out indefinite length values, "canonicalization", and tags, making it essentially MP (MP does have extension types, I should say).
https://fidoalliance.org/specs/fido-v2.0-ps-20190130/fido-cl...
[0]: https://github.com/getml/reflect-cpp/tree/main/benchmarks
As a standard it's almost exactly the same as MsgPack, the difference is mostly just that CBOR filled out underspecified parts of MsgPack. (Things like how extensions for custom types work, etc.)
Performance is just one aspect, and using poor to describe it is very misleading. Say not performant if that is what you meant.