Glossary
Webhook
A webhook is an HTTP callback that a service sends when something changes. Google and Microsoft use webhooks to notify SyncCal the moment a calendar event is created, updated, or deleted.
Webhook vs polling
Polling means the sync engine asks “anything new?” every few seconds or minutes. Webhooks invert that: the calendar provider tells the sync engine “this just changed” the instant it happens. Webhooks are faster, cheaper in API quota, and reduce sync latency to seconds.
How SyncCal uses webhooks
After you connect a Google or Microsoft calendar, SyncCal registers a webhook subscription. When you create or edit an event, the provider POSTs a small notification to a SyncCal endpoint. SyncCal then fetches the changed event and propagates it to the mirrored calendars.
When SyncCal falls back to polling
Webhook subscriptions expire (Google: 30 days max, Microsoft: 3 days for outlook.com). SyncCal renews them automatically, but if a renewal fails or the network drops a notification, an intelligent polling loop catches the change within a minute or two. CalDAV servers do not all support push notifications, so iCloud and similar use polling with adaptive intervals.
Why this matters for users
The difference between “syncs in 1 minute” and “syncs in 15 minutes” is webhook support. SyncCal optimizes for the fast path on Google and Microsoft and gracefully degrades for everything else.
If your sync feels sluggish, the issue is rarely webhook failure itself, but the underlying connection. The Why is my calendar not syncing walkthrough covers the seven failure modes worth checking before assuming the provider’s webhooks broke.