Protocol Buffers Design Skill

When to Use This Skill

Use this skill when:

• Designing gRPC services - Protocol Buffers (proto3) for typed service contracts
• Schema definition - Messages, enums, services, streaming patterns
• Implementing in C# - gRPC with ASP.NET Core
• Schema evolution - Backward/forward compatibility, versioning

MANDATORY: Documentation-First Approach

Before creating protobuf definitions:

1. Invoke docs-management skill for API contract patterns
2. Verify proto3 syntax via MCP servers (context7 for latest spec)
3. Base all guidance on Google's Protocol Buffers documentation

Why Protocol Buffers?

Benefit	Description
Efficient	Binary format, 3-10x smaller than JSON
Typed	Strong typing with code generation
Versioned	Built-in backward/forward compatibility
Cross-Language	Supports C#, Java, Python, Go, etc.
gRPC Integration	Native service definition for gRPC

Proto3 Structure Overview

syntax = "proto3";

package ecommerce.orders.v1;

option csharp_namespace = "ECommerce.Orders.V1";

import "google/protobuf/timestamp.proto";

service OrderService {
  rpc GetOrder(GetOrderRequest) returns (Order);
  rpc ListOrders(ListOrdersRequest) returns (ListOrdersResponse);
  rpc WatchStatus(WatchRequest) returns (stream StatusUpdate);
}

enum OrderStatus {
  ORDER_STATUS_UNSPECIFIED = 0;
  ORDER_STATUS_DRAFT = 1;
  ORDER_STATUS_SUBMITTED = 2;
}

message Order {
  string id = 1;
  string customer_id = 2;
  OrderStatus status = 3;
  google.protobuf.Timestamp created_at = 4;
}

For complete template: See proto-syntax.md

Quick Reference

gRPC RPC Types

Pattern	Syntax	Use Case
Unary	rpc Get(Req) returns (Resp)	Simple CRUD
Server Stream	rpc List(Req) returns (stream Resp)	Large results, updates
Client Stream	rpc Upload(stream Req) returns (Resp)	Batch uploads
Bidirectional	rpc Chat(stream Req) returns (stream Resp)	Real-time sync

For streaming patterns: See grpc-patterns.md

Naming Conventions

Element	Convention	Example
Package	lowercase.dots.version	ecommerce.orders.v1
Service	PascalCase + Service	OrderService
RPC	PascalCase verb	CreateOrder
Message	PascalCase	OrderCreatedEvent
Field	snake_case	customer_id
Enum	SCREAMING_PREFIX_VALUE	ORDER_STATUS_DRAFT

Workflow

1. Identify Resources: What entities does the service manage?
2. Define Messages: Data structures for each resource
3. Design Service Methods: CRUD operations, queries, commands
4. Add Streaming: Where real-time updates needed
5. Document: Comments for all messages and fields
6. Lint: Use Buf or protolint for consistency
7. Version: Plan for schema evolution
8. Generate: Create client/server code

References

Load on-demand based on need:

Reference	Load When
proto-syntax.md	Creating proto definitions, well-known types, advanced patterns
grpc-patterns.md	Designing streaming services (server, client, bidirectional)
csharp-implementation.md	Implementing gRPC in .NET/C# with ASP.NET Core
schema-evolution.md	Planning schema changes, Buf CLI, versioning

Related Skills (Cross-Plugin)

Phase	Skill	Plugin	Purpose
DESIGN	protobuf-design (this skill)	formal-specification	Architecture research, pattern selection
AUTHORING	N/A	spec-driven-development	Gap: protobuf-authoring not yet created

Workflow: Design (research gRPC patterns) → Author (create .proto files) → Generate (code generation)

Note: Unlike OpenAPI and AsyncAPI, protobuf authoring is typically straightforward enough that the design skill's C# implementation reference covers concrete creation. A dedicated protobuf-authoring skill may be added if demand warrants.

External References

• Protocol Buffers Documentation - Official Google documentation
• gRPC Documentation - Official gRPC guides
• Buf CLI - Modern protobuf tooling
• Google API Design Guide - Resource-oriented API patterns
• gRPC for .NET - ASP.NET Core gRPC docs

MCP Research

For current protobuf patterns and tools:

perplexity: "Protocol Buffers proto3" "gRPC service design patterns"
context7: "grpc" (for official documentation)
microsoft-learn: "gRPC ASP.NET Core" (for .NET implementation)

Version History

• v2.0.0 (2026-01-17): Refactored to progressive disclosure pattern
  • Extracted 4 reference files (~550 lines)
  • Hub reduced from 700 to ~130 lines
  • Updated NuGet package versions (Grpc.AspNetCore 2.71.0)
• v1.0.0 (2025-12-26): Initial release

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Last Updated: 2026-01-17