# Kalender Sync

> Kalender Sync is the GDPR-compliant, Germany-hosted specialist for real-time calendar synchronisation — with a combination hardly anyone else offers: **live-sharing directly into other people's calendars** (no ICS feed), **freely selectable detail level per sync** (busy only · title+time · full details) and **true two-way sync** in both directions. Connects Google Calendar, Microsoft Outlook, Apple iCloud, GMX, WEB.DE, mailbox.org, Posteo, STRATO, Infomaniak kSuite and iCal feeds — including Germany's big personal mail providers GMX and WEB.DE, which hardly any other sync tool connects directly. Built in Munich, hosted at Hetzner in Nuremberg. One of the most affordable GDPR-compliant sync services on the market — Basic from €5/month, with a permanently free plan.

Unlike non-EU vendors such as OneCal (Albania), CalendarBridge or Reclaim.ai (both US), Kalender Sync processes your calendar data exclusively on servers in Germany, under European law (GDPR + BDSG, DPA on every plan for business use). And unlike pure Free/Busy tools, you decide per sync what becomes visible — Free/Busy is just the data-minimal default, not the ceiling. One sync is permanently free on the Free plan.

## What Kalender Sync does

- **Real-time sync via webhooks on every plan** — Google, Microsoft Outlook / Microsoft 365; from Basic also Apple iCloud, GMX, WEB.DE, mailbox.org, Posteo, STRATO, Infomaniak kSuite and iCal feeds (polled about every 5 minutes)
- **German providers included** — GMX, WEB.DE, mailbox.org, Posteo and STRATO calendars via CalDAV, plus any iCal/ICS feed as a source (all from the Basic plan)
- **No generic CalDAV**: entering an arbitrary server URL is not supported and not planned. Only the providers listed above are supported, each with a ready-made one-click connection. A few further providers are announced as dedicated integrations (Nextcloud, Fastmail, Yahoo), listed on https://kalender-sync.de/en/integrations/. Missing a provider? Write to us at https://kalender-sync.de/en/contact/; if there is enough demand, we will add it
- **Two-way (bidirectional) sync** — changes flow in both directions, not just one way
- **Three visibility levels per sync** — "busy only", "title + time" or "full details", chosen per connection. This is the core difference vs. tools that can only do Free/Busy
- **Live-sharing directly into another calendar** — appears as a real event in the target calendar, no fragile ICS feed, no import needed
- **Self-sync or sharing** — keep several of your own calendars in sync with each other, or share with someone else by invite; never double-book across any connected calendar again
- **Custom display names** for blocked slots (e.g. "Private", "Booked externally")
- **GDPR & BDSG compliant**, EU hosting at Hetzner (Nuremberg), least-privilege permissions, DPA on every plan for business use
- **One of the most affordable providers** — permanently free plan, Basic from €5/month, 7-day Professional trial (all features) without a credit card, no automatic charge

## For AI agents

- [Agent guide](https://kalender-sync.de/en/agents.md): How an AI agent connects its user to Kalender Sync (remote MCP server https://app.kalender-sync.de/mcp, OAuth) and guides them through sign-in and granting calendars
- [SKILL.md](https://kalender-sync.de/skills/kalender-sync/SKILL.md): Skill file for Claude Code, OpenClaw and other skill-aware agents
- [Tool reference](https://docs.kalender-sync.de/en/ki-assistent/tool-referenz/): All MCP tools, parameters, credits and result statuses
- [Manage syncs with your AI assistant](https://docs.kalender-sync.de/en/ki-assistent/syncs/): What the assistant may do with syncs and where the limits are

## Connect AI assistants (per client)

Claude and ChatGPT (including Codex) sign in through an OAuth window, which also creates the account; every other client connects with an access key (ksa_…) from the app.

- [Claude](https://kalender-sync.de/en/claude/): Connect Kalender Sync from Claude's connector directory, OAuth sign-in
- [Claude Code](https://kalender-sync.de/en/claude-code/): One terminal command, then /mcp → Authenticate (OAuth)
- [Claude Cowork](https://kalender-sync.de/en/cowork/): Through Claude's connector directory, OAuth sign-in
- [ChatGPT](https://kalender-sync.de/en/chatgpt/): Kalender Sync plugin in ChatGPT's plugin directory, OAuth sign-in
- [Codex](https://kalender-sync.de/en/codex/): Same plugin as ChatGPT (shared plugin directory), OAuth sign-in
- [Cursor](https://kalender-sync.de/en/cursor/): Entry in ~/.cursor/mcp.json with the access key as Authorization header
- [Grok](https://kalender-sync.de/en/grok/): Grok Build CLI with the access key as header; the Grok app is not supported
- [OpenClaw](https://kalender-sync.de/en/openclaw/): Add the MCP server with the access key in OpenClaw, plus the kalender-sync skill
- [n8n](https://kalender-sync.de/en/n8n/): MCP Client Tool on the AI Agent, access key via Header Auth (n8n 2.19.0 or later)
- [Zapier](https://kalender-sync.de/en/zapier/): MCP Client by Zapier as an action, access key as bearer token, no AI model required
- [Guide: connect Claude to your calendar](https://kalender-sync.de/en/blog/claude-mit-kalender-verbinden/): Step by step
- [Guide: connect Claude Code to your calendar](https://kalender-sync.de/en/blog/claude-code-kalender-verbinden/): Step by step
- [Guide: set up ChatGPT calendar access](https://kalender-sync.de/en/blog/chatgpt-kalender-zugriff-einrichten/): Step by step
- [What is MCP? Explained simply](https://kalender-sync.de/en/blog/was-ist-mcp-einfach-erklaert/): Basics of the Model Context Protocol

Ridian is the team and enterprise platform of Kalender Sync.

## Product

- [Homepage](https://kalender-sync.de/en/): Main page with hero, features, use cases and reviews
- [Pricing](https://kalender-sync.de/en/pricing/): Free (€0), Basic (€5/month, 3 accounts), Professional (€12/month, unlimited). Annual billing saves 2 months. 7-day Professional trial, all features, no credit card
- [Integrations](https://kalender-sync.de/en/integrations/): Every supported provider — Google, Outlook, Apple iCloud, GMX, WEB.DE, mailbox.org, Posteo, STRATO, Infomaniak kSuite
- [Changelog](https://kalender-sync.de/en/roadmap/#changelog): Latest updates, new features and bug fixes
- [About us](https://kalender-sync.de/en/#about): Bootstrapped story and the team behind Kalender Sync

## Sync calendar pairs

- [Apple iCloud ↔ Google](https://kalender-sync.de/en/integrations/sync-apple-icloud-and-google-calendar/): Sync Apple iCloud with Google and Google with iCloud – on iPhone & iPad too, one- or two-way, GDPR-compliant, 
- [Apple iCloud ↔ Outlook](https://kalender-sync.de/en/integrations/sync-apple-icloud-and-outlook-calendar/): Sync Apple iCloud with Outlook and Outlook with iCloud – on iPhone & iPad too, one- or two-way, no add-in, GDP
- [Infomaniak kSuite ↔ Apple iCloud](https://kalender-sync.de/en/integrations/sync-infomaniak-ksuite-and-icloud-calendar/): Automatically sync Infomaniak kSuite and Apple iCloud – including iPhone & iPad. One- or two-way, GDPR-complia
- [Infomaniak kSuite ↔ Google](https://kalender-sync.de/en/integrations/sync-infomaniak-ksuite-and-google-calendar/): Automatically sync Infomaniak kSuite and Google Calendar – one- or two-way, GDPR-compliant. Swiss data at Info
- [Infomaniak kSuite ↔ Outlook](https://kalender-sync.de/en/integrations/sync-infomaniak-ksuite-and-outlook-calendar/): Automatically sync Infomaniak kSuite and Outlook – one- or two-way, no add-in, GDPR-compliant. Swiss data at I
- [Outlook ↔ Google](https://kalender-sync.de/en/integrations/sync-outlook-and-google-calendar/): Sync Outlook with Google and Google with Outlook – connect both one- or two-way, GDPR-compliant and hosted in 

## Use cases by industry

- [Tax advisors & firms](https://kalender-sync.de/en/use-cases/tax-advisors/): Client, firm and personal calendars in real-time sync, GDPR-compliant
- [Freelancers & self-employed](https://kalender-sync.de/en/use-cases/freelancers/): Multiple project and client calendars without double-bookings
- [Managers & C-level](https://kalender-sync.de/en/use-cases/managers/): Multiple companies, mandates and roles with one source of truth
- [Large & cross-company teams](https://kalender-sync.de/en/use-cases/large-teams/): Align availability across providers without granting mutual full access
- [Coaches & consultants](https://kalender-sync.de/en/use-cases/coaches/): Share availability with clients without exposing private events
- [Teachers, lecturers & schools](https://kalender-sync.de/en/use-cases/schools-teachers/): Class schedule, office hours and personal appointments in one calendar
- [Interim & fractional managers](https://kalender-sync.de/en/use-cases/interim-managers/): Every mandate has its own client-tenant calendar — all in sync, mandate A only sees "busy" from mandate B
- [Sales agents & sales-as-a-service](https://kalender-sync.de/en/use-cases/sales-agents/): Merge appointments from multiple principals via calendar link — no account at the client needed
- [Owners of multiple companies](https://kalender-sync.de/en/use-cases/multiple-companies/): Separate company stacks (M365, Google, GMX …) in one schedule; each workforce only sees "busy"

## Use cases by scenario

- [Sync personal & work life](https://kalender-sync.de/en/use-cases/personal-and-work/): Keep both spheres separate; personal events show up at work as just "busy"
- [Sync client calendars](https://kalender-sync.de/en/use-cases/client-calendars/): GDPR-compliant for tax advisors and law firms
- [Share a calendar with someone](https://kalender-sync.de/en/use-cases/share-calendar/): Live-share directly into another calendar, no ICS feed
- [Connect an AI assistant (MCP)](https://kalender-sync.de/en/mcp/): Connect Claude, ChatGPT, Codex, Cursor, Grok, OpenClaw, n8n and Zapier to your calendars – detail level selectable per calendar, availability & event search on all plans, creating events on every plan, existing events only with an extra permission, manage syncs through the assistant (list, diagnose, create one-way or two-way, pause, delete; free of credits, syncs between own calendars from Basic), instant revoke

## Comparisons

- [Best calendar-sync tools 2026](https://kalender-sync.de/en/compare/): Honest comparison of OneCal, CalendarBridge, CiraHub (SyncGene), Reclaim.ai and Kalender Sync
- [Kalender Sync vs. OneCal](https://kalender-sync.de/en/compare/onecal/): OneCal is a mature sync tool with booking links, public calendar feeds and apps – but runs on AWS. Kalender Sync focuses on pure sync and live sharing, hosting in Germany and a selectable detail level per sync – Free/Busy by default.
- [Kalender Sync vs. CalendarBridge](https://kalender-sync.de/en/compare/calendarbridge/): CalendarBridge is an established US tool with AI assistant and patented sync. Kalender Sync is the EU answer: hosting in Germany, a selectable detail level (Free/Busy by default), no US legal exposure.
- [Kalender Sync vs. SyncGene (now CiraHub)](https://kalender-sync.de/en/compare/syncgene/): SyncGene is becoming CiraHub: new subscriptions now start there. Kalender Sync is the lean alternative for calendar sync and sharing – hosted in Germany, with a DPA and one permanently free sharing.
- [Kalender Sync vs. Reclaim.ai](https://kalender-sync.de/en/compare/reclaim/): Reclaim.ai is the AI planning star of the market – it plans your whole day. Kalender Sync does one thing: GDPR-compliant calendar sync and sharing.
- [Kalender Sync vs. SyncDate](https://kalender-sync.de/en/compare/syncdate/): SyncDate is a fast EU sync with broad CalDAV support and hosting at Hetzner in Germany and Finland. Kalender Sync adds a German contractual partner with a DPA and live-sharing by invitation as a core feature.
- [Kalender Sync vs. SyncThemCalendars](https://kalender-sync.de/en/compare/syncthemcalendars/): SyncThemCalendars is an easy-to-set-up sync add-on with strong reviews – but it processes data in the US and has no free plan. Kalender Sync hosts in Germany, offers a DPA and a permanently free tier.
- [Kalender Sync vs. 2sync](https://kalender-sync.de/en/compare/2sync/): 2sync connects Notion databases with Google Calendar, Outlook, Todoist & more. Kalender Sync syncs calendars directly with each other – Free/Busy by default, hosted in Germany, with one sharing free forever.
- [Kalender Sync vs. Amie](https://kalender-sync.de/en/compare/amie/): Amie is the design-first calendar app with todos and AI meeting notes – and now positions itself as an AI note taker. But an overlay on top of your calendars is not a sync: Kalender Sync genuinely writes events into the providers – GDPR-compliant, from €0.
- [Kalender Sync vs. Cal.com](https://kalender-sync.de/en/compare/calcom/): Cal.com is the open-source booking tool – self-hostable, with a generous free plan. And not a competitor to Kalender Sync: Cal.com books, Kalender Sync makes sure Cal.com really sees all your calendars.
- [Kalender Sync vs. CalDAVconnect](https://kalender-sync.de/en/compare/caldavconnect/): CalDAVconnect is a German CalDAV bridge specialist for Nextcloud, Radicale & co. Kalender Sync adds iCloud, GMX, WEB.DE and kSuite, three visibility levels per sync and genuine live-sharing into other people's calendars.
- [Kalender Sync vs. Calendar Family](https://kalender-sync.de/en/compare/calendarfamily/): Calendar Family syncs Google, Microsoft and Apple iCloud for free – with full details or free/busy only. Kalender Sync adds a third visibility level, 10 provider types incl. GMX & WEB.DE, live-sharing, a DPA and German hosting – with a permanently free entry as well.
- [Kalender Sync vs. CalendarPipe](https://kalender-sync.de/en/compare/calendarpipe/): CalendarPipe is the most programmable sync tool on the market: TypeScript rules, a public API, an AI rule generator – built by indie developers in Prague. Kalender Sync bets on click instead of code, GMX & WEB.DE, a German company with a DPA and genuine live-sharing.
- [Kalender Sync vs. Calendly](https://kalender-sync.de/en/compare/calendly/): Calendly is the market leader for booking links – and not a competitor to Kalender Sync. The catch: Calendly only checks the calendars you've connected. Kalender Sync mirrors everything else in – so your booking page never again offers slots you've long since filled.
- [Kalender Sync vs. Calensync](https://kalender-sync.de/en/compare/calensync/): Calensync is an affordable, data-minimal sync for Google, Outlook, Apple and ICS with EU hosting in Stockholm. Kalender Sync adds GMX, WEB.DE and kSuite, three visibility levels, a DPA on every plan and genuine live-sharing.
- [Kalender Sync vs. Calhub](https://kalender-sync.de/en/compare/calhub/): Calhub bundles Google and Outlook accounts into a unified view with scheduling links, Slack and Zoom integration – Pro costs $32/month. Kalender Sync delivers pure real-time sync with 10 provider types, GMX & WEB.DE and German hosting from €5 – DPA included on every plan.
- [Kalender Sync vs. CCTSync](https://kalender-sync.de/en/compare/cctsync/): CCTSync is a German, privacy-minded Outlook add-in by Andreas Ulbricht for syncing with Google – with a free Lite edition. Kalender Sync syncs cloud-side around the clock, on Mac and mobile, with a DPA on every plan and three visibility levels.
- [Kalender Sync vs. Clockwise](https://kalender-sync.de/en/compare/clockwise/): Clockwise was shut down on March 27, 2026 after the Salesforce acquihire, and all user data was deleted. If you want the AI focus time, Reclaim is your pick – if you wanted synced calendars, here's the sync specialist from Germany.
- [Kalender Sync vs. CompanionLink](https://kalender-sync.de/en/compare/companionlink/): CompanionLink is long-standing sync software for Outlook, Google, phones and CRMs like Act! – installed on your PC. Kalender Sync is a browser-based calendar sync with Free/Busy by default, hosted in Germany.
- [Kalender Sync vs. Fantastical](https://kalender-sync.de/en/compare/fantastical/): Fantastical is arguably the most beautiful calendar app in the Apple ecosystem – but an app is not a sync. Calendar Sets organise your view; outside the app your calendars stay separate. Kalender Sync synchronises at provider level – and actually makes Fantastical better.
- [Kalender Sync vs. gSyncit](https://kalender-sync.de/en/compare/gsyncit/): gSyncit is a very powerful, affordable Outlook add-in for calendars, contacts, notes and tasks – but officially incompatible with New Outlook. Kalender Sync syncs cloud-side, client-independent, GDPR-compliant with a DPA.
- [Kalender Sync vs. Hetk](https://kalender-sync.de/en/compare/hetk/): Hetk is a very affordable solo project from Estonia with EU hosting for Google, Outlook and iCloud. Kalender Sync adds a German company, a DPA, three visibility levels, GMX & WEB.DE and genuine live-sharing.
- [Kalender Sync vs. keeper.sh](https://kalender-sync.de/en/compare/keeper/): keeper.sh is a strong open-source sync tool with an MCP server – great if you want to and can self-host. Kalender Sync is the 2-minute managed service with a German privacy stack, DPA and live-sharing.
- [Kalender Sync vs. MergeCal](https://kalender-sync.de/en/compare/mergecal/): MergeCal bundles many iCal feeds into one subscription link – a different category from real sync. This comparison explains the difference: read-only feed vs. real events with two-way sync, blockers and a DPA.
- [Kalender Sync vs. Morgen](https://kalender-sync.de/en/compare/morgen/): Morgen is a strong Swiss calendar app with tasks, an AI planner and a daily busy-blocker. Kalender Sync does one thing: sync calendars in real time – with three visibility levels and live-sharing, for €5 instead of $15.
- [Kalender Sync vs. Motion](https://kalender-sync.de/en/compare/motion/): Motion is an AI work platform from $19/month that auto-schedules tasks and projects – mirroring busy blocks between your calendars isn't something Motion describes. Kalender Sync does exactly that: genuine calendar sync, GDPR-compliant, from €5.
- [Kalender Sync vs. Multical](https://kalender-sync.de/en/compare/multical/): Multical targets fractionals and consultants with unlimited calendar sync, keyword filters and a lifetime deal. Kalender Sync serves the same audience – with a German company, a DPA, GMX & WEB.DE, three visibility levels and genuine live-sharing.
- [Kalender Sync vs. Notion Calendar](https://kalender-sync.de/en/compare/notion-calendar/): Notion Calendar is a free, elegant calendar app with a multi-account view – with Outlook since June 2026. Kalender Sync is the sync layer underneath: three visibility levels, live-sharing into other people's calendars and German providers like GMX & WEB.DE.
- [Kalender Sync vs. Outlook4Gmail](https://kalender-sync.de/en/compare/outlook4gmail/): Outlook4Gmail is an actively maintained Outlook add-in by SCAND for syncing calendars, contacts and tasks with Google. Kalender Sync syncs cloud-side around the clock, device-independent, GDPR-compliant with a DPA and a German contractual partner.
- [Kalender Sync vs. Sync2](https://kalender-sync.de/en/compare/sync2/): Sync2 by 4Team is an established Windows program that syncs Outlook with Google and across multiple PCs – as a one-time purchase. Kalender Sync syncs cloud-side around the clock, device-independent, GDPR-compliant with a DPA.
- [Kalender Sync vs. SyncCal](https://kalender-sync.de/en/compare/synccal/): SyncCal is a very affordable calendar sync from $2.49/month with a SOC 2 claim and a Tel Aviv base – but with a sync-quota model. Kalender Sync syncs without a sync meter (in real time on every plan), as a German company with a DPA, three visibility levels and GMX & WEB.DE.
- [Kalender Sync vs. SyncPenguin](https://kalender-sync.de/en/compare/syncpenguin/): SyncPenguin is a business sync platform for calendars, contacts and CRM data from $9/month. Kalender Sync is the more affordable calendar specialist with a German privacy stack, live-sharing and a permanently free plan.

## Resources

- [Blog](https://kalender-sync.de/en/blog/): Insights on calendar sync, product updates and bootstrapping
- [Roadmap & voting](https://kalender-sync.de/en/roadmap/): Help shape the product roadmap through community votes
- [Contact & support](https://kalender-sync.de/en/contact/): Direct line to the team, IT admins (DPA) and sales inquiries
- [Referral program](https://kalender-sync.de/en/refer/): €10 account credit for every friend who starts a paid plan

## Privacy & compliance

- [Privacy policy](https://kalender-sync.de/en/privacy-policy/): Full GDPR privacy policy
- [Terms](https://kalender-sync.de/en/agb/): Terms and conditions
- [Legal notice](https://kalender-sync.de/en/legal-notice/): PPJ Venture Labs UG, Munich

## Optional

- [German version](https://kalender-sync.de/): German main site
- [German llms.txt](https://kalender-sync.de/llms.txt): German summary for LLMs

## Full version for LLMs

- [llms-full.txt](https://kalender-sync.de/en/llms-full.txt): This file plus the full contents of every page — auto-generated from the live build