Parse an MCP JSON-RPC Message

Objective

Write a Python function that parses MCP JSON-RPC messages and extracts key information.

Background

MCP uses JSON-RPC 2.0 for communication. Every message has a specific structure that includes version, method, parameters, and an optional ID for request-response correlation.

Requirements

Create a function parse_mcp_message(message: dict) -> dict that:

1. Validates the message format: Check for required fields (jsonrpc, method)

2. Extracts message type: Determine if it's a request, response, or notification

   • Request: Has id and method
   • Response: Has id and either result or error
   • Notification: Has method but no id

3. Parses method details: Extract namespace and action from method (e.g., "tools/call" → namespace: "tools", action: "call")

4. Returns structured output:

   {
       "valid": bool,
       "type": "request" | "response" | "notification" | "invalid",
       "method": str | None,
       "namespace": str | None,
       "action": str | None,
       "id": int | str | None,
       "has_params": bool,
       "has_error": bool
   }
   

Example Input

message = {
    "jsonrpc": "2.0",
    "id": 1,
    "method": "tools/call",
    "params": {
        "name": "search",
        "arguments": {"query": "test"}
    }
}

Example Output

{
    "valid": True,
    "type": "request",
    "method": "tools/call",
    "namespace": "tools",
    "action": "call",
    "id": 1,
    "has_params": True,
    "has_error": False
}

Hints

• Use message.get("key") to safely access optional fields
• The method field uses "/" to separate namespace and action
• A response message has no method field