Mandatory
I believe the source code is here: https://chromium.googlesource.com/external/github.com/grpc/grpc/+/HEAD/src/csharp/Grpc.Tools/
Optional
Does the plugin have a valid semver version?
Yes, see here: https://www.nuget.org/packages/Grpc.Tools/
Does the plugin have a dependency on another plugin?
I don't believe so.
Does the output of this plugin depend on any other external libraries?
I don't believe so.
Motivation
There's a grpc/csharp plugin already, but it generates code that uses Grpc.Core, which is deprecated. There's an approach that uses dotnet tooling, but it'd be awesome from my perspective if Buf supported this as well.