There’s also BloomRPC, which is like Postman/Insomnia for GRPC:

https://github.com/bloomrpc/bloomrpc

And there’s Buf Studio :-) https://buf.build/blog/buf-studio https://studio.buf.build

Insomnia and Postman also support gRPC now as well. Lots of choices.

I found insomnia's grpc support a bit lacking - notably, it won't refresh the grpc definitions from disk without reloading your whole environment, and doesn't auto-populate the window with the keys. The latter is a more minor concern, but when you have larger protos it does become annoying.