CalDAV

CalDAV is an Internet standard that enables access to calendar data on a remote server using WebDAV and HTTP. It extends WebDAV with calendar-specific features and allows clients to create, read, update, and delete events and to manage calendars stored on a server. CalDAV relies on the iCalendar data format for event data.

In CalDAV, each user has one or more calendar home collections, and events are stored as VCALENDAR objects containing VEVENT components. Calendars may be organized into multiple calendars within a home collection. The protocol uses WebDAV methods such as PROPFIND and REPORT to access properties and to perform calendar queries, with the event data encoded in iCalendar format.

CalDAV supports searching calendars through calendar-query REPORT requests and can be extended to support scheduling via iTIP (iCalendar Transport-Independent Protocol) for invites and responses. While scheduling operations are defined in the iCalendar specification, CalDAV enables clients to exchange and process these objects with servers.

Security and interoperability: CalDAV deployments typically use TLS for encryption and HTTP authentication (e.g., Basic or Digest); some servers support OAuth 2.0. The protocol is widely implemented by calendar servers such as Nextcloud, Radicale, Apple Calendar Server, and Cyrus, and by clients including Apple Calendar, Mozilla Thunderbird with Lightning, and various mobile apps.

Standards and status: CalDAV is standardized by the IETF as RFC 4791 and builds on WebDAV and the iCalendar data format (RFC 5545). It remains central to interoperable calendar sharing and collaboration, though real-world interoperability depends on server and client support and on adherence to the relevant RFCs.