A Simple MCP Server And Client

🚀 A Simple MCP Server and Client

This is a simple implementation of a Model Context Protocol (MCP) server and client that demonstrates how to expose and access weather information.

🚀 Quick Start

Server

The server is implemented in the server.js file. It provides the following features:

• Resources:

  • city://NewYork: Basic information about New York City.
  • city://London: Basic information about London.
  • city://Tokyo: Basic information about Tokyo.

• Tools:

  • get-weather: Retrieve the weather forecast for a specific city, supporting the city name and the number of days as parameters.

• Prompts:

  • weather-advice: Get travel advice based on the weather conditions.

Client

The client is implemented in the client.js file. It demonstrates how to:

• Connect to the MCP server.
• List available resources.
• Read a specific city resource.
• Call the weather forecast tool.
• Get weather prompt information.

📚 Documentation

JSON-RPC Communication

This implementation uses JSON-RPC 2.0 as the underlying communication protocol between the client and the server. The key JSON-RPC concepts used include:

• Methods: Standard method names such as resources/list, resources/read, tools/call, and prompts/get.
• Parameters: Input data sent with the method call.
• Request Identifier: A unique identifier to match the response.
• Result/Error: Structured response data or error information.

The MCP SDK abstracts a large part of this, but understanding the protocol is helpful for debugging and customization. You can view the raw JSON-RPC messages by checking the console output.

Running the Server and Client

1. Start the client:

   node client.js
   

   When starting the client, the server will be automatically launched as a child process. The client will connect to the server and perform all example operations.

2. To start the server independently:

   node server.js
   

Transport Mechanism

This example uses stdio (standard input/output) as the transport mechanism between the client and the server. When the client starts, it spawns the server as a child process and communicates via the stdin/stdout streams.

A custom logging transport is implemented to display the messages exchanged between the client and the server. These messages are logged to the console in a human-readable format, which is very helpful for understanding the protocol.

Troubleshooting

If you encounter issues with resource or prompt requests timing out, please check the server implementation. The example implements direct message handling to address the limitations of the current SDK version.