CalDAV is a proposal for a standard protocol to enable calendar access via WebDAV.

The CalDAV specification was first published in 2003 by Lisa Dusseault as an Internet-Draft submitted to the Internet Engineering Task Force (IETF), and it quickly gained support from several calendaring software vendors. In January 2005 the first interoperability event was organized by the CalConnect consortium. CalDAV does not have an IETF Working Group but the authors still plan to submit it as an IETF standard. CalDAV is designed for implementation by any collaborative software, client or server, that needs to maintain, access or share collections of events. It is being developed as an open standard to foster interoperability between software from different implementors.

The architecture of CalDAV is to model events, which may be meetings or appointments or blocked-off-time, as HTTP resources. Each event is expressed in the standard ICalendar format. Thus, any Web browser can download a standard representation of an event. Events are organized into WebDAV collections to allow browsing and synchronization. In addition to HTTP (RFC2616) and WebDAV (RFC2518) functionality, a CalDAV server must support WebDAV access control (RFC3744), must parse iCalendar files (RFC2445) and support a number of calendaring-specific operations such as doing free-busy time reports and expansion of recurring events. With this functionality, a user may synchronize his or her own calendar to a CalDAV server, and share it among multiple devices or with other users. The protocol also supports non-personal calendars, such as calendars for sites or organizations.

Up-to-date CalDAV information can be found at the CalDAV home page.

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