TidyCal at present exclusively integrates with Google, Microsoft, and Apple calendars. If you use another calendar (like Fastmail) or have specific policies, preventing conflicts is impossible. Set up a custom webhook in the TidyCal API to a designated URL, which will return busy periods in JSON format for seamless calendar integration. By the way, a second webhook triggered when an appointment is scheduled would enable users to connect TidyCal with other applications beyond the native options, such as Zapier. I acquired ActivePieces from AppSumo, and it's not supported now, but by adding the scheduled-appointment webhook, it will be usable across all integration platforms.