CalDAV: Sync Calendar Data Anywhere

CalDAV is an Internet protocol based on WebDAV and used to synchronize and manage calendar data. It allows users to sync their calendars with a server, regardless of the device they are using. CalDAV is often used in email and calendar services such as Apple Calendar, Thunderbird or Nextcloud.

What is CalDAV?

The term CalDAV is the abbreviation of “ Calendar Ddistributed HASuthoring and Versioning” which can be literally translated as: “Distributed creation and versioning of calendars”. CalDAV is a network protocol first submitted to the Internet Engineering Task Force (IETF) for verification in 2003 and specified in the RFC 4791. It allows you to carry out a exchange of calendar data via WebDAV/HTTP and thus access your calendar and sync from any device. When you add new appointments or edit existing calendar entries, the changes are made automatically on all synced devices, whether PC, smartphone or tablet.

CalDAV allows you to manage and edit appointments, events and time slots on all your devices regardless of platform. In this context, this protocol manages and distributes calendar events via the HTTP transfer protocol, mainly used on the Web. All events published by CalDAV are displayed in iCalendar format, with each common browser displaying downloaded appointments or events in its iCalendar representation.

A WebDAV environment serves as the basis for management and synchronization. Thanks to CalDAV, this environment is also complemented by access control and iCalendar analysis functionalities. It is also possible to set up a blocking of writing by other users, to transmit the available dates and to merge the modifications of an entry made in parallel. Not only can you synchronize your calendar on several devices, but also the share with other users. If you also want to synchronize your contact data, you can use the CardDAV protocol.

In order to use CalDAV, you must implement the network protocol in your calendar applications by downloading and installing the CalDAV client. This program then allows you to establish a connection to the CalDAV server which acts as a central authority and regulates the exchange of calendar data.

What is a CalDAV client and CalDAV server?

A CalDAV customer is a computer program executed on a smartphone, tablet or PC which communicates with a central computer (called server) via the CalDAV protocol and thus sends and receives calendar data. Furthermore, the terminal is often called a client. The client software must not only support the network protocol, but also your device. For example, there are different clients for devices running Windows, Android or Apple.

THE CalDAV server is the counterpart of the CalDAV client: as the contact for all clients making a request, it constitutes the basis of the data exchange and the entire calendar synchronization. This means that you need a CalDAV server on which you will place your data and a suitable client on your device which will consult and display the data from the server.

Overview of the main CalDAV servers and clients

THE suitable customers for synchronizing calendar data via CalDAV include:

• CalendarSync for Android
• AgenDAV
• Atmail (versions 6.0 and above)
• Outlook CalDAV Synchronizer (free Outlook plugin)
• iPhone

For the servera basic model, offered free of charge by many providers, is sufficient for using CalDAV.

• Calendar and Contacts Server (macOS and Linux)
• Atmail (versions 6.0 and above)
• Baikal Lightweight CalDAV+CardDAV server
• Bedwork
• Google Calendar (limited support, read-only; better to use Google CalDAV API)
• ownCloud
• Nextcloud

Implementing CalDAV

If you wish set up your own CalDAV serveryou will in any case need a fixed IP address. Once the server is ready, download the CalDAV client of your choice, install it and create a account. Attach the profile to the server by indicating the relevant data such as the previously defined network address. You will then need to refine the settings by configuring the desired options, for example the people with whom you wish to share the calendar.

Using CalDAV: protocol integration examples

In organizations with mixed IT environments or individual calendar infrastructures, CalDAV makes it possible to manage appointments centrally and integrate them flexibly into existing work processes. Below we show how CalDAV can be practically integrated into popular environments such as Nextcloud, Microsoft 365 and Google Workspace.

Nextcloud: CalDAV for the private Cloud

Nextcloud supports CalDAV natively through the built-in calendar app. Users can manage their calendar data directly in the web interface and synchronize them with external clients via CalDAV. You can copy the CalDAV access URL from your calendar application user account. It generally presents itself as follows: https://cloud.example.com/remote.php/dav/calendars/username/. With a compatible CalDAV client, it is then easy to subscribe to calendars or actively edit them. Nextcloud also allows you to assign rights to shared calendars, which is ideal for teamwork.

Microsoft 365: only useful with third-party providers

Microsoft 365 does not offer native support for CalDAV. It is nevertheless possible to integrate CalDAV services via third-party tools such as CalDav Synchronizer for Outlook. These tools act as a bridge between Microsoft Exchange services and the CalDAV open standard. In companies, this method is particularly relevant when there are hybrid IT infrastructures or calendars from Nextcloud or Apple iCloud need to be combined with Outlook. However, it is possible that the functionalities or rights granted may be restricted.

THE tutorial The following explains how to use CalDav Synchronizer in Outlook:

1. Download and install the plugin. Close Outlook before installation.
2. Click the “CalDav Synchronizer” tab in Outlook and create a new CalDAV profile. Select “Generic CalDAV” as the profile type.
3. Select the Outlook folder to sync and enter your provider's CalDAV URL.
4. Save the profile to complete the setup.

Use CalDAV with Google Workspace

The CalDAV URL to access Google Workspace or Google Calendar is https://apidata.googleusercontent.com/caldav/v2/your_email_address/events. To establish the connection, you must log in to your Google accountusually via an application password or OAuth, as simple passwords are no longer accepted. You can then connect your CalDAV client to this URL to sync your appointments in read mode.

Note that Google CalDAV is mainly optimized for calendar data recovery. The complete modification of appointments is therefore often limited. For more comprehensive calendar functionality, it is recommended to use the “Google Calendar” API, which allows for more advanced management and synchronization.

Using CalDAV with IONOS

With CalDAV, IONOS also gives you an easy way to import calendar data and sync and manage it across platforms. You can therefore migrate your calendar from Webmail to Microsoft 365 and easily view and modify your appointments on different devices, without data loss or duplicates. Configuration is done via the CalDAV URL that you will find in your IONOS customer account and connection to a CalDAV-compatible calendar client.