Integrate Google Calendar with AI Assistants

Google Calendar MCP Server

A Model Context Protocol (MCP) server that provides Google Calendar integration for AI assistants like Claude.

Features

• Multi-Account Support: Connect multiple Google accounts (e.g., work, personal) and query them simultaneously
• Multi-Calendar Support: List events from multiple calendars in a single request
• Cross-Account Conflicts: Detect overlapping events across any combination of calendars
• Event Management: Create, update, delete, and search calendar events
• Recurring Events: Advanced modification capabilities for recurring events
• Free/Busy Queries: Check availability across calendars
• Smart Scheduling: Natural language understanding for dates and times
• Intelligent Import: Add calendar events from images, PDFs, or web links

Quick Start

Prerequisites

1. A Google Cloud project with the Calendar API enabled
2. OAuth 2.0 credentials (Desktop app type)

Google Cloud Setup

1. Go to the Google Cloud Console
2. Create a new project or select an existing one.
3. Enable the Google Calendar API for your project. Ensure that the right project is selected from the top bar before enabling the API.
4. Create OAuth 2.0 credentials:
   • Go to Credentials
   • Click "Create Credentials" > "OAuth client ID"
   • Choose "User data" for the type of data that the app will be accessing
   • Add your app name and contact information
   • Add the following scopes (optional):
     • https://www.googleapis.com/auth/calendar.events and https://www.googleapis.com/auth/calendar
   • Select "Desktop app" as the application type (Important!)
   • Save the auth key, you'll need to add its path to the JSON in the next step
   • Add your email address as a test user under the Audience screen
     • Note: it might take a few minutes for the test user to be added. The OAuth consent will not allow you to proceed until the test user has propagated.
     • Note about test mode: While an app is in test mode the auth tokens will expire after 1 week and need to be refreshed (see Re-authentication section below).

Installation

Option 1: Use with npx (Recommended)

Add to your Claude Desktop configuration:

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "google-calendar": {
      "command": "npx",
      "args": ["@cocal/google-calendar-mcp"],
      "env": {
        "GOOGLE_OAUTH_CREDENTIALS": "/path/to/your/gcp-oauth.keys.json"
      }
    }
  }
}

⚠️ Important Note for npx Users: When using npx, you must specify the credentials file path using the GOOGLE_OAUTH_CREDENTIALS environment variable.

Option 2: Local Installation

git clone https://github.com/nspady/google-calendar-mcp.git
cd google-calendar-mcp
npm install
npm run build

Then add to Claude Desktop config using the local path or by specifying the path with the GOOGLE_OAUTH_CREDENTIALS environment variable.

Option 3: Docker Installation

git clone https://github.com/nspady/google-calendar-mcp.git
cd google-calendar-mcp
cp /path/to/your/gcp-oauth.keys.json .
docker compose up

See the Docker deployment guide for detailed configuration options including HTTP transport mode.

First Run

1. Start Claude Desktop
2. Ask Claude to authenticate with the Google Calendar MCP server (e.g., "Authenticate with Google Calendar"). This step is required before using any calendar tool - without it, requests will fail with a -32600 error.
3. Complete the OAuth flow in your browser
4. You're ready to use calendar features!

Using Claude Code? The same steps apply - just ask Claude to authenticate with the Google Calendar MCP server from your CLI session before using any calendar tool.

Re-authentication

If you're in test mode (default), tokens expire after 7 days. If you are using a client like Claude Desktop it should open up a browser window to automatically re-auth. However, if you see authentication errors you can also resolve by following these steps:

For npx users:

export GOOGLE_OAUTH_CREDENTIALS="/path/to/your/gcp-oauth.keys.json"
npx @cocal/google-calendar-mcp auth

For local installation:

npm run auth

To avoid weekly re-authentication, publish your app to production mode (without verification):

1. Go to Google Cloud Console → "APIs & Services" → "OAuth consent screen"
2. Click "PUBLISH APP" and confirm
3. Your tokens will no longer expire after 7 days but Google will show a warning about the app being unverified.

See Authentication Guide for details.

Service Account Authentication (optional)

A service account carries its own long-lived key, so there is no browser consent step and no refresh token to expire. This is the alternative to publishing your OAuth app when the weekly re-authentication above is impractical - headless servers, containers, CI, or an app you would rather leave in Testing status.

Which calendars this works for

Sharing is what grants access - the service account is a separate identity and sees nothing by default. Domain-wide delegation is not required for the personal-calendar case; it is only needed if you want the service account to act as a user.

Limitations

• Attendees cannot be invited. The API rejects this with "Service accounts cannot invite attendees without Domain-Wide Delegation of Authority". Everything else - creating, updating, deleting, searching, free/busy - works normally.
• calendarId must be explicit. primary refers to the service account's own, empty calendar; pass the calendar's address (e.g. you@gmail.com) instead.
• list-calendars returns nothing. A calendar shared with a service account does not appear in its calendarList unless explicitly added. Address calendars by id.

Setup

1. Create a service account and a JSON key in your Google Cloud project:

   gcloud iam service-accounts create calendar-mcp --project=YOUR_PROJECT
   gcloud iam service-accounts keys create service-account.json \
     --iam-account=calendar-mcp@YOUR_PROJECT.iam.gserviceaccount.com
   

2. In Google Calendar, open Settings → your calendar → Share with specific people, add the service account's e-mail and grant "Make changes to events".

3. Point the server at the key:

   {
     "mcpServers": {
       "google-calendar": {
         "command": "npx",
         "args": ["@cocal/google-calendar-mcp"],
         "env": {
           "GOOGLE_SERVICE_ACCOUNT_KEY": "/path/to/service-account.json"
         }
       }
     }
   }
   

The key is detected by its contents ("type": "service_account"), not by a mode flag, so switching an existing install over is a one-file change. Three things are consulted, and the first one that yields an answer wins:

1. GOOGLE_SERVICE_ACCOUNT_KEY - an explicit demand for service account mode. If that file is missing, unreadable, or not a service account key, the server fails to start and says so, rather than falling back to OAuth and leaving you to guess why.
2. This server's own credentials file - GOOGLE_OAUTH_CREDENTIALS if you set it, otherwise gcp-oauth.keys.json. It is read by content, so putting a service account key at that path works. If it holds ordinary OAuth client credentials, that settles it: you have an OAuth setup, and step 3 is skipped.
3. GOOGLE_APPLICATION_CREDENTIALS - the shared Google variable, often already set for unrelated tooling. It is consulted only when this server has no credentials file of its own, so it can never silently switch a working OAuth install to a service account on the next restart. A problem with it is warned about, never fatal.

The server logs which credentials it chose, and where they came from, on every startup. Set GOOGLE_SERVICE_ACCOUNT_SUBJECT only if you are using domain-wide delegation.

Treat the key file as a credential: it does not expire. chmod 600 it, keep it out of version control, and delete the key in the Cloud Console if it is ever exposed.

Managing Multiple Accounts

Connect multiple Google accounts and use them simultaneously.

In chat (recommended): Use the manage-accounts tool to add, list, or remove accounts directly from your AI assistant - no terminal needed. See the Authentication Guide for details.

CLI: For initial setup, use npm run account auth <nickname> (e.g., npm run account auth work).

HTTP / Docker: Visit http://localhost:3000/accounts to manage accounts in the browser.

When no account parameter is supplied to a tool, read-only tools merge results from all accounts, while write tools auto-select the account with appropriate permissions.

Example Usage

Along with the normal capabilities you would expect for a calendar integration you can also do really dynamic, multi-step processes like:

1. Cross-calendar availability:

   Please provide availability looking at both my personal and work calendar for this upcoming week.
   I am looking for a good time to meet with someone in London for 1 hr.
   

2. Add events from screenshots, images and other data sources:

   Add this event to my calendar based on the attached screenshot.
   

   Supported image formats: PNG, JPEG, GIF Images can contain event details like date, time, location, and description

3. Calendar analysis:

   What events do I have coming up this week that aren't part of my usual routine?
   

4. Check attendance:

   Which events tomorrow have attendees who have not accepted the invitation?
   

5. Respond to invitations:

   Accept the team meeting invitation on my calendar for tomorrow at 2pm
   

   Decline with a note:

   Decline the Friday meeting with a note that I have a scheduling conflict
   

   Respond to recurring events:

   Accept just this week's standup, but keep future instances as tentative
   

   Decline all future Monday planning meetings
   

6. Auto coordinate events:

   Here's some availability that was provided to me by someone. {available times}
   Take a look at the times provided and let me know which ones are open on my calendar.
   

Available Tools

Documentation

• Authentication Setup - Detailed Google Cloud setup
• Advanced Usage - Multi-account, batch operations
• Deployment Guide - HTTP transport, remote access
• Docker Guide - Docker deployment with stdio and HTTP modes
• Architecture - Technical architecture overview
• Development - Contributing and testing
• Testing - Unit and integration testing guide
• Multi-Account Updates - Current status and roadmap for multi-account support

Sponsorship

If Google Calendar MCP has been useful to you and you're so inclined, I'd greatly appreciate it if you'd consider sponsoring my open source work.

Thanks! - Nate

Configuration

Environment Variables:

CLI flags take precedence over environment variables. Malformed values (for example a non-numeric PORT or an unknown TRANSPORT) stop the server at startup with an error, and the resolved configuration is logged to stderr on start.

Tool Filtering

You can limit which tools are exposed to the AI assistant using the --enable-tools flag or ENABLED_TOOLS environment variable. This is useful for:

• Reducing context usage: Each tool consumes tokens from the AI's context window. Limiting tools can help preserve context for longer conversations.
• Security: Restrict capabilities to read-only operations or specific functionality.
• Simplicity: Only expose the tools your workflow actually needs.

Via command line:

npx @cocal/google-calendar-mcp start --enable-tools list-events,create-event,get-current-time

Via environment variable in Claude Desktop config:

{
  "mcpServers": {
    "google-calendar": {
      "command": "npx",
      "args": ["@cocal/google-calendar-mcp"],
      "env": {
        "GOOGLE_OAUTH_CREDENTIALS": "/path/to/credentials.json",
        "ENABLED_TOOLS": "list-events,create-event,get-current-time,update-event"
      }
    }
  }
}

Available tool names: list-calendars, list-events, search-events, get-event, list-colors, create-event, create-events, update-event, delete-event, get-freebusy, get-current-time, respond-to-event, manage-accounts

Note: The manage-accounts tool is always available regardless of filtering, as it's needed for authentication management.

When tool filtering is active, the server provides instructions to the AI assistant listing which tools are disabled. This allows the AI to inform users that additional functionality exists but is currently unavailable, without consuming the full token cost of those tool schemas.

If the list is empty or contains only commas, the server will fail to start with an error.

If an invalid tool name is specified, the server will fail to start with an error listing all available tools.

Security

• OAuth tokens are stored securely in your system's config directory
• Credentials never leave your local machine
• All calendar operations require explicit user consent

Troubleshooting

1. OAuth Credentials File Not Found:

   • For npx users: You must specify the credentials file path using GOOGLE_OAUTH_CREDENTIALS
   • Verify file paths are absolute and accessible

2. Authentication Errors:

   • Ensure your credentials file contains credentials for a Desktop App type
   • Verify your user email is added as a Test User in the Google Cloud OAuth Consent screen
   • Try deleting saved tokens and re-authenticating
   • Check that no other process is blocking ports 3500-3505

3. Build Errors:

   • Run npm install && npm run build again
   • Check Node.js version (use LTS)
   • Delete the build/ directory and run npm run build

4. "Something went wrong" screen during browser authentication

   • Run the auth command manually (see Re-authentication above)
   • Use a Chromium-based browser. Test app authentication may not work on some non-Chromium browsers.

5. "User Rate Limit Exceeded" errors

   • This typically occurs when your OAuth credentials are missing project information
   • Ensure your gcp-oauth.keys.json file includes project_id
   • Re-download credentials from Google Cloud Console if needed
   • The file should have format: {"installed": {"project_id": "your-project-id", ...}}