Retell AI MCP Server

Instructions

Implementation Reference

• src/index.ts:1139-1140 (handler)

  Handler implementation in the executeTool switch statement: proxies the request to Retell API endpoint /create-chat with POST method and input arguments.

  case "retell_create_chat":
    return retellRequest("/create-chat", "POST", args);

• src/index.ts:201-221 (schema)

  Tool schema definition including name, description, and inputSchema used for validation and tool listing.

    name: "retell_create_chat",
    description: "Create a new chat session with a chat agent.",
    inputSchema: {
      type: "object",
      properties: {
        agent_id: {
          type: "string",
          description: "The chat agent ID to use for the session"
        },
        metadata: {
          type: "object",
          description: "Optional: Custom metadata for the chat session"
        },
        retell_llm_dynamic_variables: {
          type: "object",
          description: "Optional: Dynamic variables for personalized responses"
        }
      },
      required: ["agent_id"]
    }
  },

• src/index.ts:23-57 (helper)

  Core helper function that performs authenticated HTTP requests to the Retell API, 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();
  }

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

  MCP request handler for listing tools, returns the tools array containing the retell_create_chat schema.

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

• src/index.ts:1288-1313 (registration)

  MCP request handler for calling tools, dispatches to executeTool based on tool name.

  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,
      };
    }
  });