The technology behind calendar conflict detection in scheduling apps. How free/busy APIs, caching, and real-time checking affect booking reliability.
The Free/Busy API: The Core Technology
Google Calendar (and other providers) expose a 'free/busy' API endpoint that returns availability information for a calendar account across a time range. The API returns a list of time blocks when the calendar has events — without revealing what those events are. This privacy-preserving API is the foundation for reliable conflict detection.
Single-Calendar vs Multi-Calendar Querying
A single-calendar scheduling tool makes one API call to one calendar account. A multi-calendar tool makes parallel API calls to multiple accounts simultaneously. Cal Clear queries all connected Google Calendar accounts in parallel for each booking page load, then merges the results to find times that are free across ALL accounts.
Real-Time vs Cached Availability
Real-time scheduling tools (like Cal Clear) make fresh API calls on each page load. Cached tools store availability data and refresh it on a schedule (every 15 minutes to several hours). Real-time is more reliable but adds API call latency. Cal Clear accepts the small latency cost for the significant reliability benefit.
Edge Cases and Failure Handling
What happens if a Google Calendar API call fails? Cal Clear's design errs on the side of caution: if a calendar API call fails, the affected time slots are shown as unavailable rather than as available. This prevents false availability — better to show too little availability than to allow a double booking because a calendar check failed.
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Privacy-first scheduling with true multi-calendar conflict detection. Free forever for 1 booking link.