google-calendar-mcp-serviceaccount

A minimal MCP server that gives an AI agent read/write access to one Google Calendar, authenticated as a service account instead of through interactive OAuth.

Why a service account

Most Google Calendar MCP servers use OAuth: the app asks a human to sign in and grant consent, the way a real multi-user product would. For a personal assistant that only ever needs access to your own calendar, that's more ceremony than the job requires — publishing to production, verified domains, periodic re-consent.

A service account skips all of it: you share your calendar with the service account's email address, exactly like sharing it with another person. The credential doesn't expire until you revoke it.

Trade-off: it only works for calendars you can explicitly share by email (personal Google accounts, most Workspace setups) — it can't act broadly across a user's account the way a full OAuth grant can.

Cost: as of this writing, everything in the setup below is free — no billing account or credit card needs to be attached to the Google Cloud project. The Calendar API's free quota is far beyond what a personal assistant will ever use. This could change in the future; check current Google Cloud pricing if in doubt.

Tools

Tool	Purpose
list_events	List upcoming events in the next N days
create_event	Create an event, optionally recurring (RRULE)
update_event	Update an existing event's summary or time

No delete_event on purpose — add it yourself if you want an agent able to delete calendar entries.

Setup

Setting this up with the help of an AI coding assistant? Point it at AGENTS.md — it has the full step-by-step for both the human and the agent side.

Doing it manually:

1. In Google Cloud Console: create a project, enable the Calendar API, create a service account (not an OAuth client), download its JSON key
2. Share your Google Calendar with the service account's email address, with "Make changes to events" permission. Note the calendar's ID: for your own primary calendar this is just your email address; for any other calendar, find it under that calendar's Settings → "Integrate calendar" → "Calendar ID"
3. python3 -m venv venv && ./venv/bin/pip install -r requirements.txt
4. Copy .env.example to .env and fill in the key path and your calendar ID
5. Register calendar_server.py with your MCP client as a stdio server, passing those two variables as its environment

License

MIT — see LICENSE.