Retell AI MCP Server

Instructions

Implementation Reference

• src/index.ts:1203-1204 (handler)

  Handler case in executeTool function that performs a GET request to the Retell API endpoint /get-retell-llm/{llm_id} using the generic retellRequest helper.

  case "retell_get_llm":
    return retellRequest(`/get-retell-llm/${args.llm_id}`, "GET");

• src/index.ts:740-753 (schema)

  Input schema definition for the retell_get_llm tool, requiring llm_id parameter.

  {
    name: "retell_get_llm",
    description: "Retrieve a Retell LLM configuration.",
    inputSchema: {
      type: "object",
      properties: {
        llm_id: {
          type: "string",
          description: "The LLM configuration ID"
        }
      },
      required: ["llm_id"]
    }
  },

• src/index.ts:23-57 (helper)

  Generic helper function for making authenticated HTTP requests to the Retell AI API, used by the retell_get_llm 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();
  }

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

  Registration of the tool list handler that exposes the retell_get_llm tool (included in the tools array) via MCP protocol.

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

• src/index.ts:14-20 (helper)

  Helper function to retrieve the Retell API key from environment variable, used by retellRequest.

  function getApiKey(): string {
    const apiKey = process.env.RETELL_API_KEY;
    if (!apiKey) {
      throw new Error("RETELL_API_KEY environment variable is required");
    }
    return apiKey;
  }