ICS (iCalendar)
ICS is the standard calendar data format for exchanging events, appointments, to-dos, and free/busy information between calendar applications. It powers calendar invitations in email clients and is the foundation of CalDAV for calendar syncing.
MIME Type
text/calendar
Type
Text
Compression
Lossless
Advantages
- + Universal support in all calendar applications
- + Email clients automatically parse .ics attachments as events
- + Supports recurrence rules for repeating events
- + Subscribe to ICS URLs for live calendar feeds
Disadvantages
- − Recurrence rule (RRULE) syntax is complex and error-prone
- − Timezone handling can cause off-by-one-hour errors
- − No native support for rich formatting in event descriptions
When to Use .ICS
Use ICS for calendar event sharing, email invitations, and subscribing to event feeds.
Technical Details
ICS files are plain text with VCALENDAR and VEVENT components. Each event includes DTSTART, DTEND, SUMMARY, DESCRIPTION, LOCATION, and optional RRULE for recurrence. Timezones use VTIMEZONE or UTC offsets.
History
The IETF published iCalendar as RFC 2445 in 1998, later updated by RFC 5545 in 2009. It is supported by Google Calendar, Apple Calendar, Outlook, and every major calendar application.