In general, not nearly as mature. In general though, gRPC is not for browser->server calls (grpc-web notwithstanding) but is designed for server<->server communication.
There is some tooling out there for development (https://github.com/fullstorydev/grpcurl and https://github.com/fullstorydev/grpcui are pretty nice) but it's still much less mature than the massive amount of mature tooling available for HTTP-based services. And that is both an artifact of gRPCs relative youth compared to REST and also for some more fundamental reasons (binary wire format, mutual TLS based authentication, etc).
All that said, I've been working with gRPC over the past 6 months or so and overall the development experience is much nicer on net I think.
There is some tooling out there for development (https://github.com/fullstorydev/grpcurl and https://github.com/fullstorydev/grpcui are pretty nice) but it's still much less mature than the massive amount of mature tooling available for HTTP-based services. And that is both an artifact of gRPCs relative youth compared to REST and also for some more fundamental reasons (binary wire format, mutual TLS based authentication, etc).
All that said, I've been working with gRPC over the past 6 months or so and overall the development experience is much nicer on net I think.