While `protoc` remains the source of truth, this spec captures the syntax and rules accepted and enforced by `protoc` in a far more detailed way than the official developer site.
Buf is founded by engineers who spent a LOT of time working with Protobufs outside of Google. I was always the one saying "please don't write your own .proto parser" but I am convinced Buf actually knows what they are doing here and probably have all the details right.
Our industry has a whole lot of tooling and infrastructure built around JSON, and almost every piece of it could be way better if it were operating with well-defined types instead, in the same way that TypeScript tooling benefits vs. JavaScript. Google has had an all-protobuf ecosystem internally for a long time, but much of it will never be released publicly. So that leaves someone like Buf to really build it out. I'm pretty interested to see where they're able to take it.