Free/busy checking is the technology that makes scheduling tools actually work. Understanding it helps you choose tools that do it right — and avoid tools that do it poorly. Here's how it works and why Cal Clear's implementation is the gold standard.
What Is Free/Busy Checking?
Google Calendar (and other calendar systems) provide an API specifically for checking whether a calendar has events during specific time periods — without revealing the content of those events. This is the "free/busy" API.
When you query the free/busy API for a time slot, you get back: "this person is BUSY from 2pm-3pm" or "this person is FREE from 2pm-3pm." You don't get the event title, attendees, description, or any other details. Just busy or free.
This is privacy-preserving by design — scheduling tools can check your availability without needing to read your actual calendar content.
Cal Clear's Free/Busy Implementation
Cal Clear requests only free/busy access when you connect a Google Calendar. It never requests read access to your event content. This is a conscious privacy choice — we use the minimum permissions necessary to perform conflict detection.
When your booking page loads:
- Cal Clear identifies the time window being displayed
- For each connected Google account, Cal Clear queries Google's free/busy API
- All API queries run in parallel
- Responses are merged: any time slot that's busy on ANY connected account is marked as unavailable
- Only slots that are free on ALL connected accounts are shown to the invitee
Why Real-Time Matters for Free/Busy
Some scheduling tools request free/busy data once and cache it. This means: if you add a new event to your calendar after the cache was built, the cached availability data doesn't reflect it. The slot might still appear available on your booking page.
Cal Clear performs free/busy API calls on every booking page load — no caching of availability data. This adds a small amount of latency (the API call takes a fraction of a second) but ensures availability information is always current.
Privacy Implications
Because Cal Clear uses free/busy access (not full read access), your calendar event content stays completely private. Cal Clear knows when you're busy — it doesn't know why, with whom, or what the meeting is about. Your client appointments, personal events, and sensitive calendar content are never accessible to Cal Clear.
Frequently Asked Questions
What is free/busy calendar checking?
Free/busy checking queries your calendar to determine whether specific time slots are occupied or available, without reading the content of calendar events. Cal Clear uses Google's free/busy API to check availability across all connected calendars.
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