GRPC is rather nice. It has good and well-established practices about backwards compatibility (never ever remove a field), nullability, mapping to traditional HTTP-based endpoints, inline documentation.

The downside is that you need a special tool to accesss it, a plain browser or curl won't work.

You can use it inside a browser. Look at https://github.com/grpc/grpc-web but I agree that something like playing with curl would be impossible. I once even stumbled upon a golang project that can generates a RESTful API from your gRPC API without any modifications on your server side.

> a golang project that generates a RESTful API from your gRPC API

You might be thinking grpc-gateway. [1]

[1]: https://github.com/grpc-ecosystem/grpc-gateway