VFREEBUSY

VFREEBUSY is a component of the iCalendar data format defined in RFC 5545, the successor to RFC 2445. It enables a calendar user agent to exchange information about a person’s or resource’s availability without exposing detailed event data. A VFREEBUSY object contains a time span request and a list of free‑busy periods, allowing other users or scheduling agents to determine when the calendar owner is free, busy, tentative, or unavailable.

The component is structured as a VEVENT‑like block, beginning with “BEGIN:VFREEBUSY” and ending with “END:VFREEBUSY”. Mandatory properties include DTSTART and DTEND, which define the interval for which free‑busy information is sought. The UID property uniquely identifies the request, while DTSTAMP records the creation time. Optional properties such as ORGANIZER and ATTENDEE identify the parties involved. The free‑busy data are conveyed through one or more FREEBUSY properties, each holding one or more time intervals prefixed by the appropriate status code (FB, BUSY, BUSY‑UNAVAILABLE, BUSY‑TENTATIVE).

VFREEBUSY is commonly used by server‑based calendaring systems and email clients to provide meeting‑scheduling assistance, for example during the creation of a new meeting request where the client queries the calendars of participants. The response may be a VFREEBUSY object with populated FREEBUSY lines, or a “no data” indication if the server cannot supply the requested information.

Because VFREEBUSY does not carry detailed event descriptions, it respects privacy while still supporting automated conflict detection. Implementations must observe time‑zone handling as defined by the iCalendar specifications, and may include additional non‑standard properties for extended functionality.