An honest note up front: connecting ChatGPT to a calendar is more awkward than it should be. The official route is limited, and the flexible route hides behind a toggle called “developer mode”. This guide walks through both, so you can decide which one you actually need. It also saves you from the two pitfalls that catch almost everyone.
The official route and its limits
ChatGPT ships with an official Google Calendar connector (under Settings → Connectors). For a quick look into one Google calendar, it’s fine. But it has three limits that get annoying fast in daily use:
- Google only. Outlook, iCloud and GMX calendars stay invisible. If your work and personal life live on different providers (which describes most people), you only ever get half the truth about your availability.
- Read-only. The connector can’t create events. “Just put that in my calendar” ends in a polite refusal.
- All or nothing. You share the entire account. There’s no choice of which calendars are visible, or how much detail ChatGPT gets to see.
On top of that, the connector is a recurring topic in forums and on Reddit because for a fair number of users it simply returns nothing while showing as “connected”. Whether that hits you is luck of the draw. If it does, you’re in the right place.
The flexible route: your own MCP server in developer mode
Since 2025, ChatGPT supports the Model Context Protocol (MCP), an open standard that lets AI assistants talk to external services. (We explain what MCP is, in plain language, here.) With it, you can connect any MCP server, including one that bundles all of your calendars.
The catch: OpenAI tucks this feature away in developer mode, a beta feature flagged “higher risk”. The flag is fair, because you can point it at arbitrary servers OpenAI has never reviewed, and a malicious MCP server is a real security problem. The right response isn’t “stay away”, though. It’s: only connect servers whose operator you can identify, and where you control what gets shared. That’s exactly what our AI assistant is built around: you decide per calendar what ChatGPT sees, and you can revoke access at any time.
You’ll need a paid ChatGPT plan and a Kalender Sync account with your calendars connected. Then it goes like this:
Step 1: Enable developer mode
In ChatGPT, open Settings → Plugins and scroll all the way down to Developer mode. Flip the toggle and confirm the risk notice.
(OpenAI has renamed and moved this section several times over recent months; depending on your app version it may live under “Connectors” with an “Advanced” subsection. Search for the word “developer” and you’ll find it.)
Step 2: Add Kalender Sync as a plugin
On the plugins page, click + in the top right. In the “New plugin” dialog:
- Name:
Kalender Sync(your choice) - Connection: leave
Server URLselected and enter this address:
https://app.kalender-sync.de/mcp- Authentication:
OAuth - Confirm the risk notice and add it.
Pitfall #1: “Authentication” must be set to OAuth, not “None”. Otherwise the connection fails with an unhelpful error message, and you’ll go looking for the problem in all the wrong places.
Step 3: Grant access, deliberately
ChatGPT now sends you to our consent screen. You sign in and decide two things:
Which calendars may ChatGPT see? Calendars you don’t share don’t exist for the assistant. They never show up in any answer.
How much detail per calendar? Three levels: busy only (ChatGPT sees that you’re blocked, nothing else), title and time, or full details. “Title and time” tends to be practical for the work calendar; “busy only” is almost always enough for personal ones. Attendees, attachments and links are never transmitted on any level.
Only this confirmation creates the access. Until then, ChatGPT gets: nothing.
Pitfall #2: deleting the plugin in ChatGPT later does not revoke the access on our side. Deleting only cuts the local link. The authoritative revocation is the “Revoke” click in Kalender Sync under AI Assistant. There’s also a kill switch there that revokes everything at once.
What works now
From here on, ChatGPT answers questions across all shared calendars, read live from each provider:
- “Am I free tomorrow at 2pm?”
- “Find me a free evening this week with nothing personal scheduled either.”
- “Which three slots could I offer for a 45-minute call?”
And from the Basic plan, once you enable write access per calendar: “Block Thursday 9am for the dentist.” One hard technical boundary applies: ChatGPT can only modify or delete events it created itself. Your existing events aren’t addressable through write access, no matter what anyone prompts.
ChatGPT or Claude? An honest comparison
We support both, so we can answer this without an agenda: setup is noticeably nicer on Claude. Claude offers custom connectors as a regular, accessible feature; on ChatGPT it runs through developer mode with a beta warning sign. Once connected, the two are close to equivalent, since they speak the same protocol to the same server.
If you use both assistants: just connect both. Each access is managed and logged separately. The Claude guide is here.
Frequently asked questions
Does ChatGPT get my Google or Outlook password? No. The consent runs via OAuth with Kalender Sync; ChatGPT never sees credentials for your calendar accounts.
Is developer mode dangerous? The mode itself isn’t; untrustworthy servers are. Only connect servers from operators you can identify, ideally with granular sharing controls and an access log. You can verify both with us on the consent screen, before anything is shared.
Which calendars are supported? Google, Outlook/Microsoft 365, iCloud, GMX, WEB.DE, mailbox.org, Infomaniak KSuite and iCal feeds. All through the one connector.
What gets logged? That and what was queried, never the content of your events. You can see the log in the app; the Business plan adds CSV export.
The illustrated step-by-step version with screenshots lives in the docs. No account yet? Start free.
