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:

1. https://console.cloud.google.com/ (signed in with the account you want to authorize)
2. Select existing project (or create new one)
3. APIs & Services → Library → search Google Calendar API → Enable
4. Reuse existing OAuth consent screen / client, OR create new — Desktop app type
5. 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 alice@example.com 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.

• Site: https://skanfirmy.pl

• GitHub: https://github.com/bartosz-kuc

• Email: firma@bartosza.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.