@mindstone-engineering/mcp-server-retell-ai

Retell AI MCP Server

Voice agent phone calls, call management, agent configuration, LLM prompt management, and voice discovery via Retell AI API.

Installation

npx -y @mindstone-engineering/mcp-server-retell-ai

Or install globally:

npm install -g @mindstone-engineering/mcp-server-retell-ai
mcp-server-retell-ai

Configuration

Set the following environment variable:

Variable	Required	Description
RETELL_API_KEY	Yes	Retell AI API key. Get one at retellai.com/dashboard

MCP Host Configuration

{
  "mcpServers": {
    "retell-ai": {
      "command": "npx",
      "args": ["-y", "@mindstone-engineering/mcp-server-retell-ai"],
      "env": {
        "RETELL_API_KEY": "your-api-key"
      }
    }
  }
}

Security: outbound phone calls require host confirmation (MUST)

create_phone_call is annotated destructiveHint: true. The MCP host MUST require explicit user confirmation before invoking this tool. Outbound calls are billed per minute against your Retell AI plan and a misfired call has real-world consequences (a stranger's phone rings, a recording is captured, your account is charged) that cannot be undone.

Hosts integrating this connector are required to:

• Surface the proposed from_number and to_number to the user before each invocation.
• Block the call until the user explicitly confirms.
• Never auto-approve create_phone_call based on prior approvals — each call MUST be confirmed individually.

from_number and to_number are validated against the E.164 regex /^\+[1-9]\d{1,14}$/ before any upstream request is made. Numbers must:

• Start with +, followed by a country-code digit 1-9 (no leading zero).
• Contain only digits — spaces, dashes, parentheses are rejected.
• Be 2-15 digits long inclusive of the country code.

Malformed numbers are rejected locally with a structured INVALID_PHONE_NUMBER error and are never sent upstream.

Available Tools (15)

Phone Calls

• create_phone_call — Create an outbound phone call using a Retell AI voice agent
• create_web_call — Create a browser-based voice call with a Retell AI agent
• get_call — Get details about a specific call (status, transcript, recording)
• list_calls — List and filter calls by agent, time range, or status

Agents

• get_agent — Get full configuration of a voice agent
• list_agents — List all configured voice agents
• create_agent — Create a new voice agent
• update_agent — Update an existing agent's configuration

LLM Configuration

• update_retell_llm — Update the LLM configuration (prompt, greeting, model)
• get_retell_llm — Get the full LLM configuration
• create_retell_llm — Create a new LLM configuration
• list_retell_llms — List all LLM configurations

Discovery

• list_voices — List available text-to-speech voices
• list_phone_numbers — List registered phone numbers

Configuration

• configure_retell_api_key — Save your Retell AI API key

License

FSL-1.1-MIT