OpenRouter LangChain MCP Server

A small command-line chatbot that lets an OpenRouter model query MongoDB through a Model Context Protocol (MCP) server.

The project has two processes:

• server.js exposes MongoDB query tools over MCP stdio transport.

• client.js connects to the server, binds its tools to a LangChain OpenRouter model, and provides an interactive chat prompt.

Requirements

• Node.js 18 or newer

• A running MongoDB instance

• An OpenRouter API key

Related MCP server: mcp-mongo

Setup

1. Install dependencies:

   npm install

2. Create a .env file in the project root:

   OPENROUTER_API_KEY=your_openrouter_api_key
   MONGODB_URI=mongodb://localhost:27017

   MONGODB_URI is optional and defaults to mongodb://localhost:27017.

3. Start the interactive client:

   npm start

The client starts server.js automatically over stdio, so the MCP server does not need to be started separately.

First run

The server uses the chatbot_db database. If both the users and orders collections are missing, it creates them and inserts sample records. Existing collections are left unchanged.

The sample data includes:

• users: user IDs, names, email addresses, and statuses

• orders: order IDs, user IDs, products, and amounts

Available MCP tools

get_collections

Lists the collections in the configured MongoDB database.

query_collection

Runs a MongoDB find query. It accepts:

• collection (required): collection name, such as users or orders

• filter (optional): MongoDB filter object

• limit (optional): maximum number of documents to return; defaults to 10

Examples of questions to ask the chatbot:

Which users are active?
Show orders over $100.
What products did user 1 order?
List the available collections.

Type exit to close the client.

Configuration

The client currently uses the OpenRouter model identifier:

nvidia/nemotron-3-ultra-550b-a55b:free

To use another OpenRouter-supported model, change the model value in client.js.

Project structure

.
├── client.js   # Interactive LangChain client
├── server.js   # MCP server and MongoDB tools
├── package.json
└── README.md

Notes

• Keep .env out of version control because it contains your API key.

• The MCP server logs connection and seeding messages to stderr so they do not interfere with the stdio protocol.

• The npm start script runs client.js, which starts the MCP server automatically over stdio.

Chatbot

Users Collection

Orders Collection