honest-calendar-mcp

Local Google Calendar MCP server. Your calendar data never leaves your machine except to Google. No third party in the middle.

Companion project to honest-gmail-mcp.

Why

Most Calendar integrations for AI assistants route your event data through a hosted service that sees everything: meetings, attendees, locations, private descriptions. This one doesn't.

Data flow: You ↔ this server (on your Mac) ↔ Google Calendar API. That's it.

You can read the entire server — one file, ~250 lines of Python — and confirm exactly what it can and cannot do.

Features

Six tools exposed over MCP:

list_calendars — all calendars available on this account
list_events — events in a calendar within a time range, with optional free-text search
get_event — full details of a single event
create_event — new event (timed or all-day), with attendees, description, location, timezone
update_event — partial patch of an existing event
delete_event — delete an event

All tools that send invites accept a send_updates parameter (none by default — no email is sent unless you explicitly ask for it).

Requirements

Python 3.10+
A Google account you want to give it access to
A one-time setup in Google Cloud Console (~10 min, can reuse the OAuth client from honest-gmail-mcp if you already set that up)

Setup

1. Clone + install

git clone https://github.com/bartosz-kuc/honest-calendar-mcp.git
cd honest-calendar-mcp
python3 -m venv venv
./venv/bin/pip install -r requirements.txt

2. Get Google OAuth credentials

Same process as honest-gmail-mcp — a Desktop-app OAuth client from your own Google Cloud project. If you already have a project set up, just enable the Calendar API on it:

https://console.cloud.google.com/ (signed in with the account you want to authorize)
Select existing project (or create new one)
APIs & Services → Library → search Google Calendar API → Enable
Reuse existing OAuth consent screen / client, OR create new — Desktop app type
Save credentials.json in this repo's root directory

3. First run (does the OAuth dance)

./venv/bin/python server.py

Browser opens → sign in → Allow. Token saved locally as token.json. Press Ctrl+C after.

4. Register with your MCP client

Claude Code:

claude mcp add calendar-personal /absolute/path/to/venv/bin/python /absolute/path/to/server.py

Claude Desktop: edit claude_desktop_config.json:

{
  "mcpServers": {
    "calendar-personal": {
      "command": "/absolute/path/to/venv/bin/python",
      "args": ["/absolute/path/to/server.py"]
    }
  }
}

Example usage

"What's on my calendar tomorrow?"

AI calls list_events with tomorrow's time range → gets back events with summary, start, end, attendees.

"Book a 1h call with [email protected] next Thursday at 15:00."

AI calls create_event with summary, start, end, attendees, send_updates: "all" if you want Alice invited.

Data flow (detail)

Your AI client (Claude Code / Claude Desktop)
         ↕  MCP protocol over stdio (local process pipe)
This server (Python, on your machine)
         ↕  HTTPS to googleapis.com
Google Calendar API

No cloud middle. No telemetry. credentials.json and token.json stay on your disk and are .gitignored.

Security notes

You own the OAuth client. Nobody else can revoke, rotate, or misuse it.
Revoke anytime at https://myaccount.google.com/permissions.
Scope requested: calendar (full read/write on all your calendars). Google does not offer read-only + write-only splits for the standard Calendar scope; the write-heavy nature of a calendar-editing tool needs full scope.
No secrets in git. .gitignore blocks credentials.json, token.json, and virtualenvs.
send_updates defaults to "none" — the AI cannot accidentally spam attendees. You must explicitly ask for updates to be sent.

Author

Bartosz Kuć — Warsaw-based developer, JDG owner running skanfirmy.pl.

Consulting

Available for consulting on Polish tax and business integrations (KSeF, GUS/NFZ/GIOŚ APIs, mBank data), MCP server design, and AI-assisted tooling for JDGs and small teams. See skanfirmy.pl/uslugi for productized packages (audit 3k PLN, setup 8-15k PLN, retainer 2-4k PLN/mo), or reach out via email.

License

MIT — see LICENSE.

honest-calendar-mcp