Tool comparison

Kalender Sync vs. keeper.sh – self-hosting or managed service?

In Reddit threads about calendar sync, someone will quickly suggest "just use keeper.sh" – and rightly so: the open-source project is actively developed, technically well-built and has a genuine AI angle with its MCP server. The honest question is a different one: do you want to run a sync service – or use one? Here's a fair look at where keeper.sh shines and where Kalender Sync makes the difference.

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Background

What can keeper.sh do?

keeper.sh is an open-source calendar sync (AGPL-3.0, TypeScript) with over 1,400 GitHub stars and very active development – releases ship weekly. It aggregates events from multiple sources (Google, Microsoft Outlook/365, iCloud, Fastmail, CalDAV, ICS feeds) and pushes them into destination calendars; which fields get transferred (title, description, location, attendees) is configurable per sync. Its standout feature is a built-in MCP server that lets AI agents access connected calendars via OAuth – for reading and now also writing (creating and moving events). There's a cloud version (free with 30-minute intervals, 2 accounts and 3 connections; Pro at $5/month or $45/year with sync within seconds for Google/Outlook and within a minute for iCloud, Fastmail and CalDAV) – and when self-hosting via Docker, all Pro features are free.

Where keeper.sh is strong

Open source with full data sovereignty: AGPL-3.0, full source code on GitHub, Docker images for your own server. If you want to and can self-host, your calendar data stays 100% on your own infrastructure – and you even get all Pro features for free. That's a fair, respectable model.
MCP server for AI agents: keeper.sh ships its own MCP server: AI assistants like Claude or ChatGPT can list calendars, query events and now also create and move events via OAuth. If you want your calendar in agent workflows, this is one of the cleanest open-source solutions out there.
An active project with real momentum: Over 1,400 GitHub stars, weekly releases and a broad provider base from Google and iCloud to arbitrary CalDAV servers and ICS feeds. This is no abandoned hobby repo – it's a living project.
An affordable cloud option: If you don't want to self-host, the hosted version costs $5/month or $45/year – with sync within seconds for Google and Outlook and within a minute for iCloud, Fastmail and CalDAV. Price-wise that's on par with Kalender Sync – so the rest of the package decides.

Where Kalender Sync wins

Tap a point to see the reasoning.

Using instead of operating

Self-hosting keeper.sh means: provision a server, run a Docker stack with Postgres and Redis, register your own OAuth apps with Google and Microsoft (including Google's verification process), apply updates, set up monitoring. A feature for homelab fans – unpaid admin work for everyone else. Kalender Sync is set up in the browser in 2 minutes, and we handle operations.
A German contractual partner with a DPA

Kalender Sync is run by PPJ Venture Labs UG (haftungsbeschränkt) in Munich, hosted at Hetzner in Nuremberg, GDPR- and BDSG-compliant – with a data processing agreement for business customers. When self-hosting keeper.sh, you are the responsible operator yourself; for the keeper.sh cloud, no DPA and no EU contractual partner could be found. For tax advisors, law firms and companies with works-council agreements, that's the deciding factor.
Genuine live-sharing into other calendars

keeper.sh keeps your own accounts in sync. Kalender Sync can additionally embed your availability into another person's calendar by invitation – they accept once, and from then on everything stays current automatically. No ICS subscription, no import – real events in the target calendar.
Three visibility levels as a simple choice

keeper.sh lets you configure which fields get synced – that's good, but it's configuration work. With Kalender Sync you simply pick one of three levels per sync: "busy only", "title + time" or "full details" – and you can even set the display name a blocked slot shows up as on the other side. Data minimisation as a one-click decision, not field mapping.
10 provider types – including GMX & WEB.DE

Kalender Sync connects 10 provider types – Google, Microsoft Outlook/M365, Apple iCloud, GMX, WEB.DE, mailbox.org, Posteo, STRATO, Infomaniak kSuite and iCal feeds. And it's the only tool in this comparison with dedicated one-click GMX & WEB.DE integrations – no manual CalDAV setup with server addresses and app passwords. Your private German mail calendar runs in a controlled way right next to your work account.
Support instead of GitHub issues

With keeper.sh, the community helps you in the issue tracker – perfectly fine for a community project, but without commitments. Kalender Sync offers German-language support with a legal notice, a commercial-register entry and a team that answers when your calendar is business-critical.
A permanently free plan and fair euro pricing

One sharing is permanently free with Kalender Sync – no trial expiry, no credit card. Beyond that: Basic from €5/month, Professional at €12/month, and 7 days of all Professional features free to try. No dollar billing, no exchange-rate surprises.

When should you pick which?

keeper.sh is the right choice if:

You want to and can self-host – server, Docker, OAuth setup and updates included.
You prefer an open-source solution with full code transparency.
You want to connect your calendar to AI agents via an MCP server.
You mainly want to aggregate your own accounts and don't need sharing with third parties.

Kalender Sync is the right choice if:

You want to be up and running in 2 minutes – no server, no OAuth app, no maintenance.
You need a German contractual partner with a DPA, GDPR/BDSG compliance and Hetzner hosting.
You want to share your availability live into other people's calendars – with genuine two-way sync for your own accounts.
You want visibility per sync as a simple choice: "busy only", "title + time" or full details.
You want German providers without the tinkering: dedicated one-click integrations for Google, Microsoft Outlook/M365, Apple iCloud, GMX, WEB.DE, mailbox.org, Posteo, STRATO, Infomaniak kSuite and iCal feeds – no manual CalDAV setup with server addresses and app passwords. Kalender Sync is the only tool in this comparison with dedicated one-click GMX & WEB.DE integrations.

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Ready for calendar sync without running your own server?

Connect your calendars in a few clicks – GDPR-compliant, hosted in Germany, with genuine live-sharing. We handle the operations.

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Currently supported providers

GoogleMicrosoftApple iCloudKSuiteGMXWEB.DEmailbox.orgiCal-Feeds