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Understanding JSON-RPC 2.0 in MCP

Model Context Protocol (MCP) Server Engineering

JSON-RPC 2.0: The Language of MCP

MCP uses JSON-RPC 2.0 under the hood. Every message is a JSON object with a specific structure:

  • jsonrpc: "2.0"
  • method: The action (e.g., tools/call)
  • params: Arguments for the method
  • id: A unique identifier for the request

Example Message

{ "jsonrpc": "2.0", "id": 1, "method": "resources/list", "params": {} }

Assignment: Use the MCP Inspector to see the raw JSON-RPC messages being sent between the client and server.