Connect a CalDAV calendar to Claude and ChatGPT
Multi Calendar connects Fastmail, Zoho, GMX and other CalDAV calendars to Claude and ChatGPT with their address and password.
Multi Calendar finds Fastmail, GMX, WEB.DE, mail.com, Zoho, Yahoo and AOL calendars from the address alone, and shows where each makes the password it takes. Any other calendar server is found from your domain's records, or from the address you type.
The AI apps' own connectors
- Fastmail, Fastmail's own connector in Claude's directory, reads, creates, changes and deletes events in a Fastmail account's calendars and answers invitations. Read on 3 November 2026.
Connect it
Add it to
- 1Add to ClaudeOpens claude.ai - press Connect there.
- 2
Sign in, add your calendar and approve Claude in the window Claude opens - choose Yahoo, AOL, Fastmail, Zoho, GMX or another, type the address and paste its password when it asks
- 3
Ask Claude about your week
- 1
Run in Claude Code
/plugin marketplace add lumman-lab/multi-calendar/plugin install multi-calendar@multi-calendarRun the first, then the second.
- 2
Sign in, add your calendar and approve Claude Code on the Lumman page your browser opens - choose Yahoo, AOL, Fastmail, Zoho, GMX or another, type the address and paste its password when it asks. If none opens, run /mcp and choose multi-calendar.
- 3
Ask, or run
/multi-calendar:week
Works fully on ChatGPT Business, Enterprise and Edu.
- 1
Copy the address
- 2Open ChatGPT plugins
Press +, choose Add custom MCP server, name it Multi Calendar, paste the address, choose OAuth, tick the box and press Create as a plugin.
- 3
Install it, then sign in, add your calendar and approve on the Lumman page it opens - choose Yahoo, AOL, Fastmail, Zoho, GMX or another, type the address and paste its password when it asks. In a chat, type @ and choose Multi Calendar.
- 1
Add to
~/.cursor/mcp.json - 2
Sign in, add your calendar and approve Cursor on the Lumman page Cursor opens - choose Yahoo, AOL, Fastmail, Zoho, GMX or another, type the address and paste its password when it asks
Streamable HTTP, OAuth 2.1 with dynamic client registration. No key or client id.
- VS Code
Run MCP: Add Server, choose HTTP, paste the address and name it multi-calendar.
- Gemini CLI
gemini extensions install https://github.com/lumman-lab/multi-calendarIts first call opens Lumman's sign-in; /mcp auth multi-calendar opens it again.
- Antigravity
agy plugin install https://github.com/lumman-lab/multi-calendarRun /mcp, open multi-calendar_multi-calendar and choose Authenticate; approve on the Lumman page, then paste the code Antigravity shows back into it.
Free for every calendar you connect. Any number of booking pages and circles for $50 a year or $5 a month.
Reach and limits
- Find free time across it and every other calendar you add.
- Create, move and cancel events.
- Share booking links and a booking page, run group polls, and find a time with the people in a circle.
- A meeting with guests is made only where its server says it sends the invitations, updates and cancellations itself, from your own address.
- An invitation is answered here only where its server sends the answer - otherwise answer it from its letter or in the calendar's own app.
- Its calendars receive bookings only where its server sends invitations.
- An event keeps no privacy, out of office, focus time or video link, and shows only as busy or free.
- The calendar server has to be at a public internet address.
- AT&T and Verizon.net calendars do not connect, nor those of a company whose mail Yahoo keeps.
If it refuses
- The calendar server refused this password. Check the username and the password.
- No calendar server was found for this address. Type the server's address.
- This calendar's server does not say it sends invitations itself, so it cannot receive bookings. Choose another calendar.
Connection
- Calendar server
- Found from the address, or the one you type
- Login
- Your address, or the username you type, and the account's password or an app password
- Check
- The server accepts the password before the account is added
Your data
- Stored
- The password, encrypted under a key held outside the database
- Calendars
- No copy kept - read from the calendar on each call
- Removing it
- Disconnecting deletes our copy of the password, which works until you change or delete it at the calendar service.
Tools
- Offered
- All 21 - events_respond answers only where its server sends answers, and events_cancel cancels only an event the account organises
Everything else
Multi Calendar's address, sign-in, limits and every tool: Multi Calendar's technical details.