MCP JSON-RPC Client and Server Example

This repository contains a simple, beginner-friendly example of an MCP-inspired JSON‑RPC client and server implemented in JavaScript. The project demonstrates a basic communication flow using Node.js's built‑in modules without any external dependencies.

Overview

• Server (server.js):

  • Listens on TCP port 4000.

  • Implements two JSON‑RPC methods:

    • initialize: Returns a basic capabilities object (advertising an "echo" tool).

    • echo: Echoes back the parameters provided by the client.

• Client (client.js):

  • Connects to the server on port 4000.

  • Sends an initialize request followed by an echo request.

  • Logs the responses received from the server.

Related MCP server: Echo MCP Server

Prerequisites

• Node.js installed on your system (v10 or later is recommended).

Getting Started

Installing via Smithery

To install MCP JSON-RPC Client and Server Example for Claude Desktop automatically via Smithery:

npx -y @smithery/cli install @melvincarvalho/mcpjs --client claude

Manual Installation

1. Clone the Repository:

   git clone https://github.com/sandy-mount/mcpjs.git
   cd mcp-jsonrpc-example

2. Run the Server:

   Open a terminal window and run:

   node server.js

   You should see a message like:

   Server listening on port 4000

3. Run the Client:

   Open another terminal window and run:

   node client.js

   The client will connect to the server, send the initialize and echo requests, and display the responses.

How It Works

• The server listens for incoming TCP connections on port 4000. When it receives a JSON‑RPC message (each terminated by a newline), it processes the request:

  • For the initialize method, it returns a JSON‑RPC response with basic capabilities and server info.

  • For the echo method, it returns the parameters that were sent in the request.

  • If an unknown method is requested, it responds with a JSON‑RPC error.

• The client connects to the server, sends a JSON‑RPC initialize request, waits a short time, and then sends an echo request. Responses from the server are printed to the console.

Files

• server.js — The JSON‑RPC server implementation.

• client.js — The JSON‑RPC client implementation.

Customization

You can extend this example by:

• Adding more JSON‑RPC methods to the server.

• Implementing additional error handling and logging.

• Experimenting with different transport protocols or adding TLS support.

License

This project is licensed under the MIT License. See the LICENSE file for details.

Contributing

Feel free to open issues or submit pull requests with improvements or suggestions.

Happy coding!