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MCP (Model Context Protocol) is an open protocol designed to enable seamless integration between Large Language Model (LLM) applications and external data sources, tools, and services, similar to HTTP in networking or SMTP in email. MCP enhances the functionality, flexibility, and scalability of LLM applications by standardizing how models interact with external resources. !(#) !(#) MCP provides developers with a unified, efficient, and interoperable development environment by standardizing communication rules in the AI application ecosystem. * * * ## Core Concepts of MCP At its core, MCP focuses on **model context** - all the external information and tools that an LLM needs during its operation. MCP defines standardized interfaces and protocols, enabling LLMs to dynamically access and integrate the following: 1. **External Data Sources**: Such as databases, APIs, and document repositories, providing real-time or historical data to the LLM. 2. **Tools and Services**: Such as computation tools, search engines, and third-party services, extending the LLM's capabilities. 3. **Context Management**: Dynamically maintaining the LLM's conversation context to ensure coherence and consistency. * * * ## MCP Architecture MCP architecture consists of four key components: 1. **Host**: The host is an AI application that expects to retrieve data from a server, such as an Integrated Development Environment (IDE), chatbot, etc. The host is responsible for initializing and managing clients, handling user authorization, and managing context aggregation. 2. **Client**: The client serves as a bridge between the host and server. It maintains a one-to-one connection with the server, responsible for message routing, capability management, protocol negotiation, and subscription management. The client ensures clear, secure, and efficient communication between the host and server. 3. **Server**: The server is the component that provides external data and tools. It provides additional context and functionality for large language models through tools, resources, and prompt templates. For example, a server can provide API calls to external services like Gmail and Slack. 4. **Base Protocol**: The base protocol defines how hosts, clients, and servers communicate with each other. It includes message formats, lifecycle management, and transport mechanisms. MCP is like USB-C, allowing different devices to connect through the same interface. !(#) * * * ## How MCP Works MCP enables interaction between LLMs and external resources by defining standardized data formats and communication protocols. MCP uses JSON-RPC 2.0 as the message format, communicating through standard request, response, and notification messages. MCP supports multiple transport mechanisms, including local standard input/output (Stdio) and HTTP-based Server-Sent Events (SSE). MCP's lifecycle includes three phases: initialization, operation, and shutdown, ensuring that connection establishment, communication, and termination all comply with protocol specifications. Here is its workflow: ### 1. **Context Request** The LLM application sends a context request to external resources, containing the required data or service type. !(#) * The LLM application sends requests to external resources based on task requirements. * External resources return the required data or service results. ### 2. **Context Integration** The LLM application integrates the context data returned by external resources into the model for generating responses or executing tasks. !(#) * The LLM application combines external data with the model's internal knowledge to generate more accurate or richer responses. ### 3. **Context Management** MCP supports dynamic management of the LLM's conversation context, ensuring coherence in multi-turn dialogues. !(#) * The context manager maintains conversation history and state. * The LLM application generates coherent responses based on context. * * * ## Key Part of the Protocol - Messages At its core, MCP uses JSON-RPC 2.0 as the message format, providing a standardized way for communication between clients and servers. The base protocol defines three basic message types: Requests, Responses, and Notifications. Here is a detailed explanation of these three message types: ### 1. Requests Request messages are used to initiate operations from client to server, or from server to client. The structure of request messages is as follows: { "jsonrpc": "2.0", "id": "string | number", "method": "string", "params": { "[key: string]": "unknown" }} * **`jsonrpc`**: The protocol version, fixed at `"2.0"`. * **`id`**: A unique identifier for the request, which can be a string or number. * **`method`**: The name of the method to be called, a string. * **`params`**: The parameters of the method, an optional key-value pair object where keys are strings and values can be of any type. ### 2. Responses Response messages are replies to requests, sent from server to client, or from client to server. The structure of response messages is as follows: { "jsonrpc