I think you may be referring to JSPB. It's used internally at Google but has little support in the open-source. I know about it, but I wouldn't say I was inspired by it. It's particularly unreadable, because it needs to account for field numbers being possible sparse. Google built it for frontend-backend communication, when both the frontend and the backend use Protobuf dataclasses, as it's more efficient than sending a large JSON object and also it's faster to deserialize than deserializing a binary string on the browser side. I think it's mostly deprecated nowadays.