Glossary
ICS (iCalendar)
ICS is the standard text-based file format for calendar events. Subscribing to an .ics URL is a read-only way to pull events into a calendar app.
What ICS is
ICS files use the iCalendar format defined in RFC 5545. Each file contains one or more VEVENT blocks describing event metadata: summary, start, end, recurrence rules, attendees, and so on. Most calendar apps can import, export, and subscribe to ICS feeds.
Subscribing vs syncing
When you add an ICS URL to Google Calendar or Apple Calendar, you are subscribing read-only. The app polls the URL every few hours, and you cannot edit the events. This is fine for sports schedules and conference agendas but not for two-way sync.
Why SyncCal does not use ICS for live sync
ICS polling is too slow (hours, not minutes), read-only, and exposes the entire calendar at a single URL. Real-time sync uses CalDAV (push or short-poll) or vendor APIs (Google, Microsoft) with webhook notifications instead.
When ICS is the right tool
One-time event imports, sports and team schedules, public conference agendas, and any calendar feed published by a third party that does not offer an API.
For an ICS-based privacy workaround (publishing a “Busy only” feed instead of full event details), see method 3 in Share your calendar without showing details.