---

name: grpc description: "Build or review gRPC services and clients in .NET. USE FOR: ASP.NET Core gRPC, protobuf contracts, unary or streaming RPC, gRPC client factory, interceptors, deadlines, cancellation, channel reuse, backend service integration. DO NOT USE FOR: broad browser-facing APIs without gRPC-Web tradeoff review, SignalR realtime hubs, plain REST APIs. INVOKES: dotnet build/test and focused service or client smoke checks when code changes." compatibility: "Requires ASP.NET Core gRPC or gRPC client projects."

gRPC for .NET

Trigger On

• building backend-to-backend RPC services or clients
• adding protobuf contracts, streaming calls, or interceptors
• deciding between gRPC, HTTP APIs, and SignalR
• optimizing gRPC performance, deadlines, cancellation, or connection reuse
• integrating service-to-service communication in microservices

Do Not Use For

• public browser-first APIs unless gRPC-Web limitations are explicitly acceptable
• SignalR hub design, realtime UI fan-out, or websocket-style client collaboration
• generic ASP.NET Core minimal APIs or REST controllers with no protobuf/RPC requirement
• non-.NET gRPC work unless the user asks for cross-stack contract guidance

Load References

• references/patterns.md for proto design, streaming implementations, interceptors, health checks, load balancing, and client factory setup.
• references/anti-patterns.md for common channel, deadline, streaming, message-size, and exception-handling mistakes.

Workflow

1. Validate the architecture fit before touching code.
   • prefer gRPC for backend RPC, strong contracts, low-latency calls, or streaming
   • prefer REST or minimal APIs for broad browser compatibility and loosely coupled public APIs
   • prefer SignalR for browser/client realtime fan-out and UI collaboration
2. Treat .proto files as the source of truth.
   • keep package names, csharp_namespace, service names, and versioning deliberate
   • reserve removed field numbers and avoid reusing tags
   • use wrapper types or explicit messages when optionality matters
3. Choose the RPC shape from the interaction model.
   • unary for request/response
   • server streaming for large or progressive result sets
   • client streaming for uploads or batches
   • bidirectional streaming for coordinated two-way flows
4. Wire server and client behavior together.
   • register services with AddGrpc
   • use AddGrpcClient or long-lived GrpcChannel reuse
   • set deadlines and propagate cancellation
   • convert domain failures to appropriate RpcException status codes
5. Add observability and resilience where the boundary justifies it.
   • logging or exception interceptors
   • OpenTelemetry traces and status-code metrics
   • retry policy only for safe idempotent calls
6. Validate with the repo's normal build and tests, plus a focused smoke call when runnable.

Current Upstream Notes

• dotnet/aspnetcore v10.0.11 is servicing and does not change the gRPC programming model. Keep guidance focused on proto compatibility, streaming shape, deadlines, cancellation, channel reuse, and smoke calls.
• The August 2026 ASP.NET Core overview still treats gRPC as a contract-first RPC option. After package servicing updates, regenerate protobuf outputs only when inputs or generator packages actually changed; do not churn generated files as a proxy for validation.

flowchart LR
  A["RPC requirement"] --> B["proto contract"]
  B --> C["server implementation"]
  B --> D["client factory or channel"]
  C --> E["deadlines / cancellation / status codes"]
  D --> E
  E --> F["build, tests, smoke call"]

Examples

Use client factory for normal app integration:

builder.Services.AddGrpcClient<Greeter.GreeterClient>(options =>
{
    options.Address = new Uri("https://localhost:5001");
});

Always set a deadline and pass cancellation:

var response = await client.SayHelloAsync(
    new HelloRequest { Name = name },
    deadline: DateTime.UtcNow.AddSeconds(5),
    cancellationToken: cancellationToken);

For streaming, check cancellation inside the read/write loop and keep message sizes bounded. Load references/patterns.md before writing detailed streaming code.

Anti-Patterns

• creating a new GrpcChannel per call
• omitting deadlines and relying only on client-side cancellation
• ignoring ServerCallContext.CancellationToken in streaming handlers
• sending large single messages instead of chunking or streaming
• using gRPC as the default public browser API
• swallowing exceptions inside interceptors
• retrying non-idempotent calls without explicit policy

Deliver

• stable protobuf contracts and generated-code ownership
• service and client code that match the RPC shape
• explicit deadline, cancellation, retry, and status-code behavior
• tests or smoke checks for serialization and call behavior
• documentation of browser, transport, or deployment constraints when relevant

Validate

• dotnet build succeeds after contract or generated-code changes
• tests or smoke checks exercise at least one server/client call
• streaming methods respect cancellation and bounded message sizes
• channels are reused through client factory or a long-lived channel
• status-code handling is intentional and observable
• browser constraints are documented if gRPC-Web is involved