Retell AI MCP Server

Instructions

Implementation Reference

• src/index.ts:1145-1146 (handler)

  Handler logic within the executeTool switch statement that dispatches the tool call to Retell AI's /create-chat-completion endpoint via POST request using the shared retellRequest helper.

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

• src/index.ts:265-278 (schema)

  Input schema defining the parameters for the retell_create_chat_completion tool: required chat_id (string) and content (string).

  inputSchema: {
    type: "object",
    properties: {
      chat_id: {
        type: "string",
        description: "The chat session ID"
      },
      content: {
        type: "string",
        description: "The message content to send"
      }
    },
    required: ["chat_id", "content"]
  }

• src/index.ts:262-279 (registration)

  Tool registration in the tools array, including name, description, and input schema, which is provided to MCP clients via ListToolsRequest.

  {
    name: "retell_create_chat_completion",
    description: "Send a message in an existing chat session and get the agent's response.",
    inputSchema: {
      type: "object",
      properties: {
        chat_id: {
          type: "string",
          description: "The chat session ID"
        },
        content: {
          type: "string",
          description: "The message content to send"
        }
      },
      required: ["chat_id", "content"]
    }
  },

• src/index.ts:23-57 (helper)

  Generic helper function for making authenticated HTTP requests to the Retell AI API, used by all tool handlers including retell_create_chat_completion.

  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();
  }