Voice Call MCP Server

A Model Context Protocol (MCP) server that enables Claude and other AI assistants to initiate and manage voice calls using Twilio and OpenAI (GPT-4o Realtime model).

Use this as a base to kick-start your AI-powered voice calling explorations, save time and develop additional functionality on top of it.

Sequence Diagram

sequenceDiagram
    participant AI as AI Assistant (e.g., Claude)
    participant MCP as MCP Server
    participant Twilio as Twilio
    participant Phone as Destination Phone
    participant OpenAI as OpenAI
    
    AI->>MCP: 1) Initiate outbound call request <br>(POST /calls)
    MCP->>Twilio: 2) Place outbound call via Twilio API
    Twilio->>Phone: 3) Ring the destination phone
    Twilio->>MCP: 4) Call status updates & audio callbacks (webhooks)
    MCP->>OpenAI: 5) Forward real-time audio to OpenaAI's realtime model
    OpenAI->>MCP: 6) Return voice stream
    MCP->>Twilio: 7) Send voice stream
    Twilio->>Phone: 8) Forward voice stream
    Note over Phone: Two-way conversation continues <br>until the call ends

Features

• Make outbound phone calls via Twilio 📞
• Process call audio in real-time with GPT-4o Realtime model 🎙️
• Real-time language switching during calls 🌐
• Pre-built prompts for common calling scenarios (like restaurant reservations) 🍽️
• Automatic public URL tunneling with ngrok 🔄
• Secure handling of credentials 🔒

Why MCP?

The Model Context Protocol (MCP) bridges the gap between AI assistants and real-world actions. By implementing MCP, this server allows AI models like Claude to:

1. Initiate actual phone calls on behalf of users
2. Process and respond to real-time audio conversations
3. Execute complex tasks requiring voice communication

This open-source implementation provides transparency and customizability, allowing developers to extend functionality while maintaining control over their data and privacy.

Requirements

• Node.js >= 22
  • If you need to update Node.js, we recommend using nvm (Node Version Manager):

    nvm install 22
    nvm use 22
    

• Twilio account with API credentials
• OpenAI API key
• Ngrok Authtoken

Installation

Manual Installation

1. Clone the repository

   git clone https://github.com/lukaskai/voice-call-mcp-server.git
   cd voice-call-mcp-server
   

2. Install dependencies and build

   npm install
   npm run build
   

Configuration

The server requires several environment variables:

• TWILIO_ACCOUNT_SID: Your Twilio account SID
• TWILIO_AUTH_TOKEN: Your Twilio auth token
• TWILIO_NUMBER: Your Twilio number
• OPENAI_API_KEY: Your OpenAI API key
• NGROK_AUTHTOKEN: Your ngrok authtoken
• RECORD_CALLS: Set to "true" to record calls (optional)

Claude Desktop Configuration

To use this server with Claude Desktop, add the following to your configuration file:

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json

Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "voice-call": {
      "command": "node",
      "args": ["/path/to/your/mcp-new/dist/start-all.cjs"],
      "env": {
        "TWILIO_ACCOUNT_SID": "your_account_sid",
        "TWILIO_AUTH_TOKEN": "your_auth_token",
        "TWILIO_NUMBER": "your_e.164_format_number",
        "OPENAI_API_KEY": "your_openai_api_key",
        "NGROK_AUTHTOKEN": "your_ngrok_authtoken"
      }
    }
  }
}

After that, restart Claude Desktop to reload the configuration. If connected, you should see Voice Call under the 🔨 menu.

Example Interactions with Claude

Here are some natural ways to interact with the server through Claude:

1. Simple call:

Can you call +1-123-456-7890 and let them know I'll be 15 minutes late for our meeting?

2. Restaurant reservation:

Please call Delicious Restaurant at +1-123-456-7890 and make a reservation for 4 people tonight at 7:30 PM. Plea

... [View full README on GitHub](https://github.com/popcornspace/voice-call-mcp-server#readme)