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

Web application

The webapp/ directory contains a browser-based version of the chatbot. It runs an Express server, serves the UI from webapp/public/index.html, and exposes the chat endpoint at POST /api/chat.

The webapp runs the MCP server and client in the same Node.js process using an in-memory transport. The browser can therefore use the same MongoDB tools as the command-line client without starting a separate MCP process.

Run the webapp

1. Install the webapp dependencies:

   cd webapp
   npm install

2. Create a .env file in the webapp/ directory:

   OPENROUTER_API_KEY=your_openrouter_api_key
   MONGODB_URI=mongodb://localhost:27017
   PORT=3000

   MONGODB_URI defaults to mongodb://localhost:27017, and PORT defaults to 3000.

3. Start the server:

   node server.js

4. Open http://localhost:3000 in a browser.

Webapp behavior

• The UI accepts natural-language questions about the MongoDB database.

• Tool calls made by the model are displayed in the conversation.

• The final model response is displayed after the tool calls complete.

• Press Enter to send a message, or use the Send button.

• The API returns { reply, steps } for successful requests and { error } for failures.

Example request:

curl -X POST http://localhost:3000/api/chat \
  -H "Content-Type: application/json" \
  -d '{"message":"Show me active users"}'

Webapp project structure

webapp/
├── public/
│   └── index.html   # Browser chat interface
├── package.json
└── server.js        # Express app, MCP tools, and chat API

The webapp uses the same chatbot_db database and sample users and orders collections described above. Keep the .env file out of version control because it contains the OpenRouter API key.

Webapp