Kalender Sync

Kalender Sync is a German‑hosted service that synchronises your personal and work calendars automatically. It connects Outlook, Google, Apple iCloud, GMX, WEB.DE, mailbox.org, Posteo, KSuite, Nextcloud and STRATO, and runs in real‑time either one‑way or two‑way. The platform is advertised as GDPR‑compliant and starts at 5 € per month for the Basic plan, with a 50 % discount on the first year if you sign up before 27 October with the code PH50.

During your first connection you pick the calendars you want to sync and set the visibility for each one. The options are: “busy only”, “title + time” or “full details”. If you grant write access the calendars can be updated by the service and by any connected AI agent. The API endpoint for the sync service is https://app.kalender-sync.de/mcp. Integration is available for several AI platforms: Claude, ChatGPT, Codex, Grok, Cursor and OpenClaw. Each integration has a simple instruction set; for example, a Claude user copies a small command that adds the Kalender Sync server to the assistant's transport configuration, while a ChatGPT user installs the Kalender Sync plugin and follows the onboarding flow. When an agent is connected, it can read your calendar entries and create new ones, using the visibility level you chose. The agent receives calendar data in JSON, and can post events back to the same endpoint.

The free trial lasts seven days and does not ask for a credit card; it allows you to test syncs with the calendars you own. After the trial the Basic plan costs 5 € per month, and a Premium or Professional plan is available but the pricing and limits for that plan are not disclosed on the page. The service's privacy policy notes that all data stays within German borders, but no further details on data retention or access logs are provided.

Kalender Sync is suitable for individuals or small teams who already use a mix of the supported email/calendar services and want one source of truth for all meetings. It can also be useful for AI developers who need a reliable, real‑time calendar source for an assistant. The service may not be ideal for users who rely on calendar providers that are not listed (e.g., Microsoft 365 outside Outlook, or proprietary private calendars).