Retell AI MCP Server

Instructions

Implementation Reference

• src/index.ts:1247-1248 (handler)

  Switch case in executeTool function that handles the retell_get_voice tool by making a GET request to the Retell API endpoint `/get-voice/{voice_id}`.

  case "retell_get_voice":
    return retellRequest(`/get-voice/${args.voice_id}`, "GET");

• src/index.ts:1004-1017 (schema)

  Tool definition in the tools array, including name, description, and input schema requiring 'voice_id'.

  {
    name: "retell_get_voice",
    description: "Retrieve details of a specific voice.",
    inputSchema: {
      type: "object",
      properties: {
        voice_id: {
          type: "string",
          description: "The voice ID to retrieve"
        }
      },
      required: ["voice_id"]
    }
  },

• src/index.ts:23-57 (helper)

  Generic helper function that performs authenticated HTTP requests to the Retell AI API, used by all tool handlers including retell_get_voice.

  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();
  }

• src/index.ts:1283-1285 (registration)

  Registration of the ListToolsRequestSchema handler that returns the full list of tools, including retell_get_voice.

  server.setRequestHandler(ListToolsRequestSchema, async () => {
    return { tools };
  });

• src/index.ts:1287-1313 (registration)

  Registration of the CallToolRequestSchema handler which dispatches to executeTool based on tool name, enabling execution of retell_get_voice.

  // Register tool execution handler
  server.setRequestHandler(CallToolRequestSchema, async (request) => {
    const { name, arguments: args } = request.params;
  
    try {
      const result = await executeTool(name, args as Record<string, unknown>);
      return {
        content: [
          {
            type: "text",
            text: JSON.stringify(result, null, 2),
          },
        ],
      };
    } catch (error) {
      const errorMessage = error instanceof Error ? error.message : String(error);
      return {
        content: [
          {
            type: "text",
            text: `Error: ${errorMessage}`,
          },
        ],
        isError: true,
      };
    }
  });