Retell AI MCP Server

Instructions

Implementation Reference

• src/index.ts:1261-1262 (handler)

  Handler implementation for the retell_register_phone_call tool. It invokes the generic retellRequest helper to POST to the Retell API endpoint /register-phone-call with the provided arguments.

  case "retell_register_phone_call":
    return retellRequest("/register-phone-call", "POST", args);

• src/index.ts:1094-1115 (schema)

  Input schema definition for the retell_register_phone_call tool, specifying required parameters: agent_id, from_number, to_number, and optional metadata.

  inputSchema: {
    type: "object",
    properties: {
      agent_id: {
        type: "string",
        description: "The agent ID to handle the call"
      },
      from_number: {
        type: "string",
        description: "The caller's phone number"
      },
      to_number: {
        type: "string",
        description: "The called number"
      },
      metadata: {
        type: "object",
        description: "Optional metadata for the call"
      }
    },
    required: ["agent_id", "from_number", "to_number"]
  }

• src/index.ts:1091-1116 (registration)

  Tool definition and registration in the static tools array used for ListTools response.

  {
    name: "retell_register_phone_call",
    description: "Register an inbound call from a custom telephony provider.",
    inputSchema: {
      type: "object",
      properties: {
        agent_id: {
          type: "string",
          description: "The agent ID to handle the call"
        },
        from_number: {
          type: "string",
          description: "The caller's phone number"
        },
        to_number: {
          type: "string",
          description: "The called number"
        },
        metadata: {
          type: "object",
          description: "Optional metadata for the call"
        }
      },
      required: ["agent_id", "from_number", "to_number"]
    }
  }

• src/index.ts:23-57 (helper)

  Generic helper function for making authenticated API requests to Retell AI, used by the tool handler.

  async function retellRequest(
    endpoint: string,
    method: string = "GET",
    body?: Record<string, unknown>
  ): Promise<unknown> {
    const apiKey = getApiKey();
  
    const headers: Record<string, string> = {
      "Authorization": `Bearer ${apiKey}`,
      "Content-Type": "application/json",
    };
  
    const options: RequestInit = {
      method,
      headers,
    };
  
    if (body && method !== "GET") {
      options.body = JSON.stringify(body);
    }
  
    const response = await fetch(`${RETELL_API_BASE}${endpoint}`, options);
  
    if (!response.ok) {
      const errorText = await response.text();
      throw new Error(`Retell API error (${response.status}): ${errorText}`);
    }
  
    // Handle 204 No Content
    if (response.status === 204) {
      return { success: true };
    }
  
    return response.json();
  }