How to integrate Google Calendar MCP with Mastra AI

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Introduction

This guide walks you through connecting Google Calendar to Mastra AI using the Composio tool router. By the end, you'll have a working Google Calendar agent that can create a meeting with the marketing team, list all events scheduled for next week, delete tomorrow’s canceled event from my calendar, update the time for friday’s project sync through natural language commands.

This guide will help you understand how to give your Mastra AI agent real control over a Google Calendar account through Composio's Google Calendar MCP server.

Before we dive in, let's take a quick look at the key ideas and tools involved.

TL;DR

Here's what you'll learn:
  • Set up your environment so Mastra, OpenAI, and Composio work together
  • Create a Tool Router session in Composio that exposes Google Calendar tools
  • Connect Mastra's MCP client to the Composio generated MCP URL
  • Fetch Google Calendar tool definitions and attach them as a toolset
  • Build a Mastra agent that can reason, call tools, and return structured results
  • Run an interactive CLI where you can chat with your Google Calendar agent

What is Mastra AI?

Mastra AI is a TypeScript framework for building AI agents with tool support. It provides a clean API for creating agents that can use external services through MCP.

Key features include:

  • MCP Client: Built-in support for Model Context Protocol servers
  • Toolsets: Organize tools into logical groups
  • Step Callbacks: Monitor and debug agent execution
  • OpenAI Integration: Works with OpenAI models via @ai-sdk/openai

What is the Google Calendar MCP server, and what's possible with it?

The Google Calendar MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your Google Calendar account. It provides structured and secure access to your calendars and events, so your agent can schedule meetings, create or modify events, list upcoming appointments, and manage calendars—all on your behalf.

  • Automated event creation and scheduling: Easily instruct your agent to add new events, meetings, or reminders with specific times, attendees, and details.
  • Event listing and agenda overview: Have your agent list all upcoming, past, or filtered events on any of your calendars to keep you on top of your schedule.
  • Calendar management and customization: Direct your agent to create new calendars, update calendar details, or even insert calendars into your list for better organization.
  • Event updating and deletion: Let your agent modify existing events or remove events that are no longer needed, keeping your calendar up to date.
  • Complete calendar clearing: Ask your agent to clear all events from a primary calendar or delete secondary calendars entirely when you need a fresh start.

Supported Tools & Triggers

Tools
Triggers
Insert Calendar into ListInserts an existing calendar into the user's calendar list.
Update Calendar List EntryUpdates an existing entry on the user\'s calendar list.
Delete CalendarDeletes a secondary calendar.
Update CalendarUpdates metadata for a calendar.
Clear CalendarClears a primary calendar.
Create EventCreates an event on a google calendar, needing rfc3339 utc start/end times (end after start) and write access to the calendar.
Delete eventDeletes a specified event by `event id` from a google calendar (`calendar id`); this action is idempotent and raises a 404 error if the event is not found.
Create a calendarCreates a new, empty google calendar with the specified title (summary).
Get Event InstancesReturns instances of the specified recurring event.
List EventsReturns events on the specified calendar.
Move EventMoves an event to another calendar, i.
Watch EventsWatch for changes to events resources.
Find eventFinds events in a specified google calendar using text query, time ranges (event start/end, last modification), and event types; ensure `timemin` is not chronologically after `timemax` if both are provided.
Find free slotsFinds free/busy time slots in google calendars for specified calendars within a defined time range (defaults to the current day utc if `time min`/`time max` are omitted), enhancing busy intervals with event details; `time min` must precede `time max` if both are provided.
Query Free/Busy InformationReturns free/busy information for a set of calendars.
Get Google CalendarRetrieves a specific google calendar, identified by `calendar id`, to which the authenticated user has access.
Get current date and timeGets the current date and time, allowing for a specific timezone offset.
List ACL RulesRetrieves the list of access control rules (acls) for a specified calendar, providing the necessary 'rule id' values required for updating specific acl rules.
List Google CalendarsRetrieves calendars from the user's google calendar list, with options for pagination and filtering.
Patch CalendarPartially updates (patches) an existing google calendar, modifying only the fields provided; `summary` is mandatory and cannot be an empty string, and an empty string for `description` or `location` clears them.
Patch EventUpdates specified fields of an existing event in a google calendar using patch semantics (array fields like `attendees` are fully replaced if provided); ensure the `calendar id` and `event id` are valid and the user has write access to the calendar.
Quick Add EventParses natural language text to quickly create a basic google calendar event with its title, date, and time, suitable for simple scheduling; does not support direct attendee addition or recurring events, and `calendar id` must be valid if not 'primary'.
Remove attendee from eventRemoves an attendee from a specified event in a google calendar; the calendar and event must exist.
List SettingsReturns all user settings for the authenticated user.
Watch SettingsWatch for changes to settings resources.
Sync EventsSynchronizes google calendar events, performing a full sync if no `sync token` is provided or if a 410 gone error (due to an expired token) necessitates it, otherwise performs an incremental sync for events changed since the `sync token` was issued.
Update ACL RuleUpdates an access control rule for the specified calendar.
Update Google eventUpdates an existing event by `event id` in a google calendar; this is a full put replacement, so provide all desired fields as unspecified ones may be cleared or reset.

What is the Composio tool router, and how does it fit here?

What is Tool Router?

Composio's Tool Router helps agents find the right tools for a task at runtime. You can plug in multiple toolkits (like Gmail, HubSpot, and GitHub), and the agent will identify the relevant app and action to complete multi-step workflows. This can reduce token usage and improve the reliability of tool calls. Read more here: Getting started with Tool Router

The tool router generates a secure MCP URL that your agents can access to perform actions.

How the Tool Router works

The Tool Router follows a three-phase workflow:

  1. Discovery: Searches for tools matching your task and returns relevant toolkits with their details.
  2. Authentication: Checks for active connections. If missing, creates an auth config and returns a connection URL via Auth Link.
  3. Execution: Executes the action using the authenticated connection.

Step-by-step Guide

Prerequisites

Before starting, make sure you have:
  • Node.js 18 or higher
  • A Composio account with an active API key
  • An OpenAI API key
  • Basic familiarity with TypeScript

Getting API Keys for OpenAI and Composio

OpenAI API Key
  • Go to the OpenAI dashboard and create an API key.
  • You need credits or a connected billing setup to use the models.
  • Store the key somewhere safe.
Composio API Key
  • Log in to the Composio dashboard.
  • Go to Settings and copy your API key.
  • This key lets your Mastra agent talk to Composio and reach Google Calendar through MCP.

Install dependencies

bash
npm install @composio/core @mastra/core @mastra/mcp @ai-sdk/openai dotenv

Install the required packages.

What's happening:

  • @composio/core is the Composio SDK for creating MCP sessions
  • @mastra/core provides the Agent class
  • @mastra/mcp is Mastra's MCP client
  • @ai-sdk/openai is the model wrapper for OpenAI
  • dotenv loads environment variables from .env

Set up environment variables

bash
COMPOSIO_API_KEY=your_composio_api_key_here
COMPOSIO_USER_ID=your_user_id_here
OPENAI_API_KEY=your_openai_api_key_here

Create a .env file in your project root.

What's happening:

  • COMPOSIO_API_KEY authenticates your requests to Composio
  • COMPOSIO_USER_ID tells Composio which user this session belongs to
  • OPENAI_API_KEY lets the Mastra agent call OpenAI models

Import libraries and validate environment

typescript
import "dotenv/config";
import { openai } from "@ai-sdk/openai";
import { Agent } from "@mastra/core/agent";
import { MCPClient } from "@mastra/mcp";
import { Composio } from "@composio/core";
import * as readline from "readline";

import type { AiMessageType } from "@mastra/core/agent";

const openaiAPIKey = process.env.OPENAI_API_KEY;
const composioAPIKey = process.env.COMPOSIO_API_KEY;
const composioUserID = process.env.COMPOSIO_USER_ID;

if (!openaiAPIKey) throw new Error("OPENAI_API_KEY is not set");
if (!composioAPIKey) throw new Error("COMPOSIO_API_KEY is not set");
if (!composioUserID) throw new Error("COMPOSIO_USER_ID is not set");

const composio = new Composio({
  apiKey: composioAPIKey as string,
});
What's happening:
  • dotenv/config auto loads your .env so process.env.* is available
  • openai gives you a Mastra compatible model wrapper
  • Agent is the Mastra agent that will call tools and produce answers
  • MCPClient connects Mastra to your Composio MCP server
  • Composio is used to create a Tool Router session

Create a Tool Router session for Google Calendar

typescript
async function main() {
  const session = await composio.create(
    composioUserID as string,
    {
      toolkits: ["googlecalendar"],
    },
  );

  const composioMCPUrl = session.mcp.url;
  console.log("Google Calendar MCP URL:", composioMCPUrl);
What's happening:
  • create spins up a short-lived MCP HTTP endpoint for this user
  • The toolkits array contains "googlecalendar" for Google Calendar access
  • session.mcp.url is the MCP URL that Mastra's MCPClient will connect to

Configure Mastra MCP client and fetch tools

typescript
const mcpClient = new MCPClient({
    id: composioUserID as string,
    servers: {
      nasdaq: {
        url: new URL(composioMCPUrl),
        requestInit: {
          headers: session.mcp.headers,
        },
      },
    },
    timeout: 30_000,
  });

console.log("Fetching MCP tools from Composio...");
const composioTools = await mcpClient.getTools();
console.log("Number of tools:", Object.keys(composioTools).length);
What's happening:
  • MCPClient takes an id for this client and a list of MCP servers
  • The headers property includes the x-api-key for authentication
  • getTools fetches the tool definitions exposed by the Google Calendar toolkit

Create the Mastra agent

typescript
const agent = new Agent({
    name: "googlecalendar-mastra-agent",
    instructions: "You are an AI agent with Google Calendar tools via Composio.",
    model: "openai/gpt-5",
  });
What's happening:
  • Agent is the core Mastra agent
  • name is just an identifier for logging and debugging
  • instructions guide the agent to use tools instead of only answering in natural language
  • model uses openai("gpt-5") to configure the underlying LLM

Set up interactive chat interface

typescript
let messages: AiMessageType[] = [];

console.log("Chat started! Type 'exit' or 'quit' to end.\n");

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
  prompt: "> ",
});

rl.prompt();

rl.on("line", async (userInput: string) => {
  const trimmedInput = userInput.trim();

  if (["exit", "quit", "bye"].includes(trimmedInput.toLowerCase())) {
    console.log("\nGoodbye!");
    rl.close();
    process.exit(0);
  }

  if (!trimmedInput) {
    rl.prompt();
    return;
  }

  messages.push({
    id: crypto.randomUUID(),
    role: "user",
    content: trimmedInput,
  });

  console.log("\nAgent is thinking...\n");

  try {
    const response = await agent.generate(messages, {
      toolsets: {
        googlecalendar: composioTools,
      },
      maxSteps: 8,
    });

    const { text } = response;

    if (text && text.trim().length > 0) {
      console.log(`Agent: ${text}\n`);
        messages.push({
          id: crypto.randomUUID(),
          role: "assistant",
          content: text,
        });
      }
    } catch (error) {
      console.error("\nError:", error);
    }

    rl.prompt();
  });

  rl.on("close", async () => {
    console.log("\nSession ended.");
    await mcpClient.disconnect();
    process.exit(0);
  });
}

main().catch((err) => {
  console.error("Fatal error:", err);
  process.exit(1);
});
What's happening:
  • messages keeps the full conversation history in Mastra's expected format
  • agent.generate runs the agent with conversation history and Google Calendar toolsets
  • maxSteps limits how many tool calls the agent can take in a single run
  • onStepFinish is a hook that prints intermediate steps for debugging

Complete Code

Here's the complete code to get you started with Google Calendar and Mastra AI:

typescript
import "dotenv/config";
import { openai } from "@ai-sdk/openai";
import { Agent } from "@mastra/core/agent";
import { MCPClient } from "@mastra/mcp";
import { Composio } from "@composio/core";
import * as readline from "readline";

import type { AiMessageType } from "@mastra/core/agent";

const openaiAPIKey = process.env.OPENAI_API_KEY;
const composioAPIKey = process.env.COMPOSIO_API_KEY;
const composioUserID = process.env.COMPOSIO_USER_ID;

if (!openaiAPIKey) throw new Error("OPENAI_API_KEY is not set");
if (!composioAPIKey) throw new Error("COMPOSIO_API_KEY is not set");
if (!composioUserID) throw new Error("COMPOSIO_USER_ID is not set");

const composio = new Composio({ apiKey: composioAPIKey as string });

async function main() {
  const session = await composio.create(composioUserID as string, {
    toolkits: ["googlecalendar"],
  });

  const composioMCPUrl = session.mcp.url;

  const mcpClient = new MCPClient({
    id: composioUserID as string,
    servers: {
      googlecalendar: {
        url: new URL(composioMCPUrl),
        requestInit: {
          headers: session.mcp.headers,
        },
      },
    },
    timeout: 30_000,
  });

  const composioTools = await mcpClient.getTools();

  const agent = new Agent({
    name: "googlecalendar-mastra-agent",
    instructions: "You are an AI agent with Google Calendar tools via Composio.",
    model: "openai/gpt-5",
  });

  let messages: AiMessageType[] = [];

  const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
    prompt: "> ",
  });

  rl.prompt();

  rl.on("line", async (input: string) => {
    const trimmed = input.trim();
    if (["exit", "quit"].includes(trimmed.toLowerCase())) {
      rl.close();
      return;
    }

    messages.push({ id: crypto.randomUUID(), role: "user", content: trimmed });

    const { text } = await agent.generate(messages, {
      toolsets: { googlecalendar: composioTools },
      maxSteps: 8,
    });

    if (text) {
      console.log(`Agent: ${text}\n`);
      messages.push({ id: crypto.randomUUID(), role: "assistant", content: text });
    }

    rl.prompt();
  });

  rl.on("close", async () => {
    await mcpClient.disconnect();
    process.exit(0);
  });
}

main();

Conclusion

You've built a Mastra AI agent that can interact with Google Calendar through Composio's Tool Router. You can extend this further by:
  • Adding other toolkits like Gmail, Slack, or GitHub
  • Building a web-based chat interface around this agent
  • Using multiple MCP endpoints to enable cross-app workflows

How to build Google Calendar MCP Agent with another framework

OpenAI Agents SDK

OpenAI Agents SDK

Use Google Calendar MCP with OpenAI Agents SDK

Claude Agent SDK

Claude Agent SDK

Use Google Calendar MCP with Claude Agent SDK

Google ADK

Google ADK

Use Google Calendar MCP with Google ADK

LangChain

LangChain

Use Google Calendar MCP with LangChain

Vercel AI SDK

Vercel AI SDK

Use Google Calendar MCP with Vercel AI SDK

LlamaIndex

LlamaIndex

Use Google Calendar MCP with LlamaIndex

CrewAI

CrewAI

Use Google Calendar MCP with CrewAI

FAQ

What are the differences in Tool Router MCP and Google Calendar MCP?

With a standalone Google Calendar MCP server, the agents and LLMs can only access a fixed set of Google Calendar tools tied to that server. However, with the Composio Tool Router, agents can dynamically load tools from Google Calendar and many other apps based on the task at hand, all through a single MCP endpoint.

Can I use Tool Router MCP with Mastra AI?

Yes, you can. Mastra AI fully supports MCP integration. You get structured tool calling, message history handling, and model orchestration while Tool Router takes care of discovering and serving the right Google Calendar tools.

Can I manage the permissions and scopes for Google Calendar while using Tool Router?

Yes, absolutely. You can configure which Google Calendar scopes and actions are allowed when connecting your account to Composio. You can also bring your own OAuth credentials or API configuration so you keep full control over what the agent can do.

How safe is my data with Composio Tool Router?

All sensitive data such as tokens, keys, and configuration is fully encrypted at rest and in transit. Composio is SOC 2 Type 2 compliant and follows strict security practices so your Google Calendar data and credentials are handled as safely as possible.

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