There's grpcurl and other similar tools for when you just want to run a simple gRPC request against a server. If you server runs the reflection service, it will also let you inspect the schema of whatever is running on a given endpoint.

For in-browser use with gRPCweb, if you use test-proto-on-XHR, things continue to work as with REST/JSON.

For inter-server debugging, you usually defer to opentracing or similar, and capture request data there.