iCalendar

iCalendar (RFC 5545) is the Internet Calendaring and Scheduling Core Object Specification — the standard data format for representing and exchanging calendaring and scheduling information. It defines a text-based format for calendar events (VEVENT), to-do items (VTODO), journal entries (VJOURNAL), free/busy information (VFREEBUSY), and time zone definitions (VTIMEZONE).

What You Need to Know

At its core, an iCalendar object is a collection of properties and components encoded in a plain-text format (often stored in .ics files). Each calendar component contains properties that describe it — start and end times, summaries, descriptions, attendees, recurrences, and more.

Key concepts for developers:

• Components — VEVENT, VTODO, VJOURNAL, VFREEBUSY, and VTIMEZONE are the primary building blocks.
• Properties — Each component has properties like DTSTART, DTEND, SUMMARY, UID, and RRULE that define its behavior.
• Recurrence rules — The RRULE property enables complex repeating patterns (daily, weekly, monthly, yearly) with exceptions and modifications.
• Time zone handling — iCalendar can represent times as UTC, local (floating), or with explicit time zone references using VTIMEZONE.