cal-sync
Mirror busy blocks across every Google Calendar you have, so any scheduling tool sees your true cross-account availability.
A small always-on service that watches every Google Calendar I have and mirrors events between them as opaque “Busy” blocks. Cal.com, Calendly, Reclaim.ai, and Google’s own find a time now see my real availability across work, personal, and side-project calendars — without paying for the multi-calendar tier of any of them.
What I was solving
I run on three Google accounts. The scheduling tools I use are excellent at checking one calendar for conflicts on their free tiers, and want $10–15/month per seat to check more. Multiply by every product (Cal.com Pro, Calendly Standard, Reclaim Starter) and the “let people book me without double-bookings” feature was about to cost more than the rest of my software stack combined. cal-sync solves that one specific problem at the calendar layer instead — every tool keeps seeing one calendar, but that one calendar now reflects everything.
How it works
Cloudflare Workers + D1 (SQLite) + Queues, kicked by Google’s push notifications. When an event changes on calendar A, the worker writes a placeholder event titled Busy (a@example.com) on calendars B and C — copying only the start and end time. No titles, attendees, or details ever cross between calendars. Loop prevention uses both an extendedProperties tag and a sync-mapping table; either layer alone is enough to recognize and skip our own writes. Recurring series, moved instances, and cancelled instances all propagate correctly.
The tricky parts ended up being (a) cleanly handling the case where one connected account’s OAuth token gets revoked (one broken account shouldn’t poison the rest of the mesh) and (b) backfilling the right direction when a new account is added (the new calendar’s events have to flow out and existing calendars’ events have to flow in, both at the same time).
Status
Live at cal-sync.tozca.com. Multi-tenant — anyone can sign in with Google and get an isolated workspace; per-user mirror counts in the dashboard show the system is doing what it claims (~50 mirrors flowing across my four accounts at any given moment). Privacy and terms drafted against Google’s OAuth verification checklist for restricted Calendar scope.