Protocol Selector Protocol

This skill prevents the "Golden Hammer" anti-pattern (where every problem is solved with GraphQL just because it's trendy, or REST just because it's familiar). It selects the correct transport layer based on the actual consumer needs.

Core assumption: There is no single "best" protocol. Picking gRPC for a public frontend is a disaster; picking REST for high-frequency microservice-to-microservice communication is inefficient.

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1. Requirement Analysis (Static)

Analyze the system context based on user inputs:

• Clients: Web Browser? Mobile App? Internal Microservices? IoT Devices?
• Data Shape: Highly relational/graph-like? Binary files? Simple CRUD?
• Delivery Expectation: Request/Response? Server-to-Client Push? Bi-directional streams?

2. Trade-Off Evaluation

Map requirements to the strengths of specific protocols:

• 🌐 REST (HTTP/JSON): Best for public external APIs. Easy to cache, ubiquitous, simple tooling. Bad for over-fetching.
• 🕸️ GraphQL: Best for complex frontends and mobile apps needing to aggregate data from multiple sources. Prevents over-fetching. Hard to cache, risk of N+1 problems.
• ⚡ gRPC / Protocol Buffers: Best for internal microservices. Binary, heavily compressed, strongly typed, fast. Extremely difficult for browsers to consume natively.
• 📡 WebSockets: Best for true bi-directional real-time communication (e.g., Chat, Multiplayer Games). Stateful, difficult to scale and load balance.
• 📥 Server-Sent Events (SSE): Best for uni-directional real-time updates (e.g., Live sports scores, progress bars, notifications). Simpler to scale than WebSockets, runs over standard HTTP.

3. Output Generation

Required Outputs (Must write BOTH to docs/api-report/):

1. Human-Readable Markdown (docs/api-report/protocol-selection-report.md)

### 🏛️ API Protocol Selection

**Context:** Building a live-updating dashboard for IoT sensor data and an internal admin CRUD panel.

#### 🎯 Recommended Architecture: Hybrid (REST + SSE)

**1. CRUD Operations: REST**
- **Why:** The admin panel performs standard Create/Read/Update/Delete operations on devices. Caching is useful here. Predictable tooling.
- **Trade-off:** Potential over-fetching on the dashboard list view, but acceptable for admin use.

**2. Live Sensor Data: Server-Sent Events (SSE)**
- **Why:** The dashboard only needs to *receive* live updates from the sensors. It doesn't need to push data back constantly. SSE is much lighter on infrastructure than WebSockets.
- **Trade-off:** Uni-directional only. If the frontend needs to send a command, it must use a standard REST `POST`.

2. Machine-Readable JSON (docs/api-report/protocol-selection-output.json)

{
  "skill": "protocol-selector",
  "primary_protocol": "REST",
  "secondary_protocol": "SSE",
  "reasoning": "Standard CRUD best served by REST, live read-only dashboard best served by SSE to avoid WS overhead.",
  "rejected_protocols": ["gRPC (Ext. facing)", "GraphQL (No complex joins req)"]
}

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Guardrails

• Beware the gRPC Web Trap: If suggesting gRPC for a web frontend, you MUST mention grpc-web and Envoy proxies as a major infrastructure overhead.
• GraphQL Caching: If suggesting GraphQL, explicitly mention that standard HTTP caching (CDN) will not work easily; application-level caching (e.g., Apollo Client) is required.