The Model Context Protocol (MCP) is a foundational client-server communication standard designed to enable seamless interaction between Large Language Model (LLM) applications and their integrations. It establishes a robust framework for exchanging context, tools, and prompts.
At its core, MCP operates on a client-server architecture where:
* **Hosts** are LLM applications (e.g., Claude Desktop, IDEs) that initiate connections.
* **Clients** are components within the host application that maintain 1:1 connections with servers.
* **Servers** provide the necessary context, tools, and prompts to clients.
The protocol is built upon two main layers:
1. **Protocol Layer**: Manages message framing, request/response linking, and high-level communication patterns, defining how messages are structured and exchanged.
2. **Transport Layer**: Handles the actual communication, supporting mechanisms like Stdio for local processes and HTTP with Server-Sent Events (SSE) for remote communication. All transports utilize JSON-RPC 2.0 for message exchange.
MCP defines four primary message types:
* **Requests**: Messages that expect a response.
* **Results**: Successful responses to requests.
* **Errors**: Indicate a failed request.
* **Notifications**: One-way messages that do not expect a response.
The connection lifecycle involves a clear sequence:
1. **Initialization**: Client and server exchange capabilities and acknowledge readiness.
2. **Message Exchange**: Normal request-response and notification patterns occur.
3. **Termination**: Either party can gracefully close the connection.
MCP includes defined error handling mechanisms with standard error codes and emphasizes best practices for transport selection, message handling, security (e.g., TLS for remote connections, input validation), and debugging/monitoring through logging and diagnostics. Understanding MCP's architecture is crucial for developing and integrating LLM applications effectively.
