Claude Voice Callback MCP Server

An MCP (Model Context Protocol) server that enables Claude to call users back after completing long-horizon tasks, delivering results and receiving next instructions via voice.

The Problem

When Claude works on long-horizon tasks (refactoring large codebases, multi-step research, complex debugging), users have to:

• Stay at their terminal watching progress
• Periodically check if Claude is done
• Context-switch repeatedly between their work and Claude

The solution: User says "call me when you're done", walks away, and Claude calls them with results.

Installation

npm install claude-voice-callback

Or use directly with npx:

npx claude-voice-callback

Configuration

Add to your Claude Code MCP configuration (~/.claude/mcp.json or project-level .mcp.json):

{
  "mcpServers": {
    "voice-callback": {
      "command": "npx",
      "args": ["claude-voice-callback"],
      "env": {
        "VOICE_CALLBACK_API_URL": "https://your-backend.com/api/voice_callback",
        "VOICE_CALLBACK_API_KEY": "your-api-key"
      }
    }
  }
}

Tools

voice_callback_register

Register a phone number for voice callbacks at the start of a session.

Parameters:

• phone_number (required): Phone number in E.164 format (e.g., +15551234567)
• client_info (optional): Metadata about the client

Example:

Claude: I'll register your phone number for callbacks.
[Uses voice_callback_register with phone_number: "+15551234567"]

voice_callback_notify

Call the user with a summary of completed work and an optional question.

Parameters:

• summary (required): What Claude accomplished (read aloud by Claudius)
• question (optional): Question to ask the user

Example:

Claude: I've finished the refactoring. Let me call you with the results.
[Uses voice_callback_notify with summary: "I've refactored the auth module..."]

voice_callback_await

Wait for the user's voice response after initiating a call.

Parameters:

• timeout_minutes (optional): Max wait time in minutes (default: 5)

Returns:

• response: Transcribed user response (if answered)
• no_answer: Boolean if user didn't answer
• waiting: Boolean if still waiting

voice_callback_end

End the callback session when done.

Example Usage

User: "My number is 555-123-4567. Refactor the database layer
       to use connection pooling. Call me when done."

Claude:
1. Registers phone: voice_callback_register("+15551234567")
2. Works on task (15-30 minutes)
3. Calls user: voice_callback_notify(
     summary: "I've implemented connection pooling across 8 files...",
     question: "Should I commit this, or run load tests first?"
   )
4. Waits for response: voice_callback_await()
5. Receives: "Run the load tests and then commit if they pass"
6. Continues working...
7. Ends session: voice_callback_end()

Backend Requirements

This MCP server requires a backend service that handles:

• Session management
• Twilio integration for outgoing calls
• Ultravox integration for voice AI
• Webhook handling for call events

See the main repository for backend deployment options.

Environment Variables

| Variable | Description | Default | |----------|-------------|---------| | VOICE_CALLBACK_API_URL | Backend API base URL | http://localhost:8000/api/voice_callback | | VOICE_CALLBACK_API_KEY | API key for authentication | (none) |

License

MIT