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name: mcp-fundamentals description: core architecture of the Model Context Protocol (MCP). Use this to understand Hosts, Clients, Servers, and the JSON-RPC communication layer.

MCP Fundamentals

Goal

Understand the Model Context Protocol (MCP) architecture to solve the "$N \times M$" integration problem, decoupling AI models from the specific implementation details of external tools.

Core Architectural Components

1. The Host (The Application)

• Definition: The container application (e.g., a desktop app, IDE, or agent platform) that manages the user experience and orchestrates tool usage.
• Responsibilities:
  • Creating and managing MCP clients.
  • Enforcing security policies and content guardrails.
  • Managing the user interaction lifecycle.

2. The Client (The Connector)

• Definition: A software component embedded within the Host that maintains a 1:1 connection with a specific Server.
• Responsibilities:
  • Issuing commands to the server.
  • Receiving and processing responses or notifications.
  • Managing the session lifecycle.

3. The Server (The Provider)

• Definition: A standalone program that exposes capabilities (Tools, Resources, Prompts) to the AI application.
• Responsibilities:
  • Tool Discovery: Advertising what tools are available.
  • Execution: Receiving commands and running the actual logic/API calls.
  • Formatting: Returning standardized results to the client.

The Communication Layer

Protocol: JSON-RPC 2.0

All communication is text-based and language-agnostic, relying on four standard message types:

1. Requests: Calls expecting a response (e.g., tools/call).
2. Results: Successful responses containing data.
3. Errors: Failure messages with codes and descriptions.
4. Notifications: One-way messages requiring no response (e.g., logging).

Transport Mechanisms

• stdio (Standard Input/Output):
  • Use Case: Local, private tools.
  • Mechanism: The Host spawns the Server as a subprocess and communicates via standard I/O pipes. Best for accessing local files or scripts.
• Streamable HTTP (SSE):
  • Use Case: Remote or distributed tools.
  • Mechanism: Uses Server-Sent Events (SSE) for streaming responses, allowing connections to remote services over standard HTTP.