MCP clients

Model Context Protocol (MCP) Concepts

• MCP Client Purpose: Acts as the communication bridge between the main server and the MCP server (the tool access point).
• Transport Agnostic: MCP is designed to communicate over various protocols, not just one.
• Communication Methods:
• Standard Input/Output (I/O) (common when client and server are on the same machine).
• HTTP
• WebSockets
• Other defined techniques.
• Communication Mechanism: Communication occurs through the exchange of defined messages specified in the MCP spec.

Core Message Types

• Tool Discovery:
• Client sends: List Tools Request (asks the server for available tools).
• Server responds: List Tools Result (provides the list of tools).
• Tool Execution:
• Client sends: Call Tool Request (asks the server to run a specific tool with arguments).
• Server responds: Call Tool Result (contains the output/result of the tool execution).

The Complex Workflow (Tool Use Example)

The process of using an external tool (e. g. , GitHub) involves multiple steps between the user, the server, the client, and the MCP server:

• User Query: User submits a query to the main server.
• Tool Discovery: The server asks the MCP Client for a list of available tools.
• Client → MCP Server (List Tools Request)
• MCP Server → Client (List Tools Result)
• Tool Selection: The server sends the user query and the tool list to the MCP Server (e. g. , Claude/LLM).
• Tool Request: The MCP Server determines a tool is needed and sends a tool use message.
• Tool Execution: The main server asks the MCP Client to run the required tool.
• Client → MCP Server (Call Tool Request)
• MCP Server executes the tool (e. g. , queries GitHub).
• MCP Server → Client (Call Tool Result)
• Final Response: The main server sends the tool result back to the MCP Server (LLM) within a user message, allowing the LLM to formulate a final, informed response to the user.

Takeaways

• The MCP Client serves as the communication bridge between the main server and the MCP server, which is the tool access point.
• MCP is transport agnostic, meaning it is designed to communicate over various protocols including Standard I/O, HTTP, and WebSockets.
• Core communication relies on defined message types: Tool Discovery (List Tools Request/Result) and Tool Execution (Call Tool Request/Result).
• Tool use follows a complex, multi-step workflow where the server requests tools, the MCP Server selects them, the Client executes them, and the result is fed back to the MCP Server for a final response.