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The Calendar system in Sailfish OS allows users to view, create, and share calendar events, and to schedule reminders for various events. Event information from a variety of sources is separated in the database into distinct calendar collections.


The Calendar stack in Sailfish OS includes several API components. All of the native API components are fully open-source.

Platform API

Sailfish OS currently uses the mKCal extensions to the KCalCore API as its platform API. Sailfish OS is currently the defacto upstream for mKCal, which was open-sourced by Nokia previously, while KCalCore is a well-maintained KDE API.

There are plans in the future to switch to using the QtPIM QtOrganizer API as the platform API, however this requires three steps: first, an mKCal backend for the QtOrganizer API could be written during the transition phase; second, an sqlite-based QtOrganizer backend could be implemented directly; finally, the QtProject would need to release the QtPIM API in an official release. At this stage, the platform API is not available to third-party developers to use in native applications, due to the plan to switch to the QtPIM API in the future.

The KCalCore repository can be found at:

The mKCal repository can be found at:

The QtPIM QtOrganizer API (currently in tech-preview status) can be found at:

UI Layer API

A set of QML bindings for the platform API have been written to allow calendar and event information to be accessed and modified in QtQuick applications on Sailfish OS. These APIs have been developed specifically for Sailfish OS and the Nemo Mobile project, and are fully open-source. The repository also includes tools to inspect, import, and export calendar event information.

The nemo-qml-plugin-calendar repository can be found at:

Android Compatibility

Calendar data is shared with Android applications which have been allowed the appropriate permissions by the user, via a device-local bridge database. Android applications can access that information via the normal Android APIs once they have been granted permission by the user.

Storage And Middleware

Sailfish OS includes a variety of middleware pieces related to the calendar domain, and specific storage and synchronization implementations exist for the platform.

Storage Backend

The mKCal platform API also includes an sqlite-based storage backend. There are plans to migrate way from mKCal eventually, for reasons of maintainability, and as part of that process two things would occur: first, a QtOrganizer backend could use mKCal as its storage provider during a transition phase; second, a native QtOrganizer sqlite backend could be written specifically to take advantage of the performance and maintainability improvements which would result.


As with other data-related domains, synchronization of calendar data is controlled by Buteo (the synchronization framework used in SailfishOS). Synchronization with a variety of data sources is supported through a number of data-source-specific synchronization plugins. Each plugin is independent, although many of them share significant amounts of code to ease maintenance.

The various synchronization plugins are listed below:


Community or third-party contributions to various components of the location and positioning stack in Sailfish OS is encouraged and appreciated. The vast majority of the components are open-source, found on, with discussions via IRC (#sailfishos via and via email.

Specifically, contributions would be very welcome in the following areas:

  • unit test improvements both for the current platform API and mKCal storage backend, and for synchronization plugins
  • test accounts on CalDAV instances
  • test robots to perform smoke testing for synchronization plugins
  • implementation of a native, sqlite-based QtOrganizer backend

For in-depth information about contributing to the CalDAV synchronisation plugin, please see CalDAV and CardDAV Community Contributions.