# What is Kalender Sync?
Kalender Sync keeps your calendars in the loop with each other: events from one calendar automatically appear as blockers in another — in your own calendars or someone else's. You decide exactly how much is visible: just "busy", title and time, or full details.
This solves the classic multi-calendar problem: nobody books a meeting into a slot that has long been taken in another calendar.
## Video: Kalender Sync explained
## Two ways to use Kalender Sync
- **[Share calendar](https://docs.kalender-sync.de/en/sharings/share-with-others/)** — you share your availability with another person (colleague, partner, assistant). They receive an email invitation and choose for themselves which calendar your blockers go into.
- **[Sync calendar](https://docs.kalender-sync.de/en/sharings/self-sync/)** — you link two of your own calendars, e.g. work and personal. One-way or both ways (available on Basic and up).
Good to know:
- Events always flow from the **source into the target**. If two calendars should block each other, set the sync up in both directions.
- Your **original events are never modified** — Kalender Sync only creates its own blocker events in the target and manages exclusively those.
- When you end a sync, all blockers created by Kalender Sync are **cleaned up** in the target.
## You control what's visible
For each sync you pick one of three [visibility levels](https://docs.kalender-sync.de/en/sync/visibility-levels/):
| Level | What arrives in the target |
| --- | --- |
| **Busy only** (default) | Just the time slot, with a neutral title — maximum privacy |
| **Title + time** | Event name plus start and end time |
| **Full details** | Incl. location, description, notes and links |
At **no** level are attendee lists, email addresses, organisers or accept/decline responses transferred — that's third-party data and stays out. More under [Security & privacy](https://docs.kalender-sync.de/en/privacy-it/security-overview/).
## Supported calendars
| Provider | Connection | Plan | Sync speed |
| --- | --- | --- | --- |
| 
Google Calendar | Sign in with your account (OAuth) | Free | almost instant* |
| 
Microsoft Outlook / 365 | Sign in with your account (OAuth) | Free | almost instant* |
| 
Apple iCloud | App-specific password | Basic+ | every few minutes |
| 
GMX | App-specific password | Basic+ | every few minutes |
| 
WEB.DE | App-specific password | Basic+ | every few minutes |
| 
mailbox.org | Application password | Basic+ | every few minutes |
| 
Infomaniak KSuite | App password | Basic+ | every few minutes |
| 
iCal/ICS feeds | Feed URL (source only) | Basic and up | every few minutes |
\* Real-time via webhooks on Basic and up; on the Free plan, syncs run every 30 minutes.
Missing your provider? Email [support@kalender-sync.de](mailto:support@kalender-sync.de) — we can enable most providers within a few days.
Details and guides: [Connect your first calendar](https://docs.kalender-sync.de/en/getting-started/connect-first-calendar/).
## What Kalender Sync deliberately is not
- **Not a calendar merge**: your calendars are not combined — each calendar stays as it is; only blockers are added.
- **Not a booking tool**: Kalender Sync doesn't hand out booking links. It makes sure booking tools and colleagues see your real availability.
- **Not a data collector**: event contents are never stored permanently — they only pass through during sync. Hosted in Germany.
## Next steps
1. [Create an account & sign in](https://docs.kalender-sync.de/en/getting-started/create-account/)
2. [Connect your first calendar](https://docs.kalender-sync.de/en/getting-started/connect-first-calendar/)
3. [Create your first sharing](https://docs.kalender-sync.de/en/getting-started/first-sharing/)
Received an **invitation**? This way: [I received an invitation](https://docs.kalender-sync.de/en/getting-started/received-invite/).