All 15 gRPC Services questions
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How do you define a gRPC service contract using Protocol Buffers, and how is the C# service implementation generated from it?

Intermediate

Answer

A .proto file defines the service's RPC methods and message types using protobuf syntax; the Grpc.Tools NuGet package's build-time code generation (via <Protobuf Include="..." /> in the .csproj) automatically generates a strongly-typed C# base class (GreeterBase) that you inherit from and override to implement the actual service logic, plus a strongly-typed client class for consumers.
// greet.proto
service Greeter {
  rpc SayHello (HelloRequest) returns (HelloReply);
}

// GreeterService.cs -- inherits generated base class
public class GreeterService : Greeter.GreeterBase {
    public override Task<HelloReply> SayHello(HelloRequest request, ServerCallContext context) {
        return Task.FromResult(new HelloReply { Message = $"Hello {request.Name}" });
    }
}

// Program.cs
app.MapGrpcService<GreeterService>();
Real-world example A payments microservice defines its contract in a shared .proto file checked into a common repository, generating both the C# server implementation stub and client code automatically, ensuring server and client never drift out of sync on the contract shape.

Common follow-ups: How do you version a .proto contract without breaking existing clients?;How is the generated code shared between multiple services/repositories?

API Versioning;API Documentation with Swagger/OpenAPI
All 15 gRPC Services questions