Yes indeed - it's actually pretty nice. You just define a message for your configuration schema:

  message Config {
    repeated Server server = 1;
  }

  message Server {
    string address = 1;
    int32 port = 2;
    bool standby = 3;
  }

And then you use the text representation in a config file:

  # main instance
  server { address: "127.0.0.1" port: 4567 }
  # backup instance
  server { address: "127.0.0.1" port: 9876 standby: true }

And load it into a message instance:

  Config config;
  google::protobuf::TextFormat::ParseFromString(input, &config);

Unfortunately, it is undocumented and has no formal spec, and this appears to be intentional, with no plans for improvement: https://github.com/protocolbuffers/protobuf/issues/3755.

Wow, I use pb's a ton and didn't know this. I'd upvote this twice if I could!

It looks oddly like HCL. I wonder...

As of protobuf 3 they also have a canonical JSON representation, which you can access from all the supported languages.