Simple MCP Client with LangGraph Agent

A lightweight implementation of a multiserver MCP (Model Context Protocol) client using a LangGraph agent with Express.js and TypeScript.

Features

- Express.js server with TypeScript
- LangGraph agent for handling conversations
- MCP client for tool integration
- Streaming responses

Setup

1. Clone the repository
2. Install dependencies:
npm install
3. Create a .env file with the following variables:

   PORT=3000

   NODE_ENV=development

   CORS_ORIGIN=*

   ANTHROPIC_API_KEY=your_anthropic_api_key

   

API Endpoints

Initialize Chat

GET /api/chat/init

Generate Chat

POST /api/chat

Request body:

{
  "input": "Hello, how can you help me?",
  "characterId": "character_123",
  "llmConfig": {
    "model": "claude-3-opus-20240229",
    "verbose": true
  },
  "chatHistory": [],
  "mcpServers": [
    {
      "name": "weather-service",
      "version": "1.0",
      "url": "https://example-mcp-server.com",
      "key": "optional_api_key"
    }
  ]
}

Close Chat

GET /api/chat/close

MCP Integration

The server connects to MCP servers specified in the request and retrieves available tools that can be used by the LangGraph agent.

Development

Run the development server with auto-reload:

npm run dev

Example Usage

// Send a message and stream the response
const response = await fetch("/api/chat", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    input: "What's the weather in New York?",
    characterId: "agent1",
    chatHistory: [],
    mcpServers: [
      {
        name: "weather-service",
        version: "1.0",
        url: "https://my-mcp-server.com",
      },
    ],
  }),
});
// Read the streaming response

const reader = response.body.getReader();

while (true) {

  const { done, value } = await reader.read();

  if (done) break;

  const text = new TextDecoder().decode(value);

  const events = text.split("\n\n").filter(Boolean);

  for (const event of events) {

    const data = JSON.parse(event);

    console.log(data);

  }

}