For those looking for such features, Insomnia has support with some limitations.
<a href="https://docs.insomnia.rest/insomnia/grpc" rel="nofollow">https://docs.insomnia.rest/insomnia/grpc</a>
Looks interesting, but there doesn’t seem to be any licence on this project, and it is not clear if the source is available via the repo linked from website. Anyone know if this is FOSS?