Cronofy API vs Google Calendar API

Cronofy API

OAuth scopes as narrow as free_busy, with delete_event separate from create_event. Production pricing starts at $819 a month billed yearly.

Google Calendar API

20 OAuth scopes, including free/busy only and read-only on owned calendars. Google calendars only.

Cronofy API

1. Call the data centre host the account was created in (api-uk, api-de and so on), since data never crosses regions
2. Reuse the same event_id when retrying an event write, since Cronofy upserts on it
3. Ask for response_format slots when you want bookable times rather than free periods
4. On 423, ask the user to relink, since Cronofy has already emailed them
5. Keep under 50 requests a second and 500 a minute, and pause on 429

Google Calendar API

1. Ask for calendar.events.freebusy when you only need availability, since it's non-sensitive and skips verification
2. Set your own event id on insert, and treat a 409 as already created
3. Use singleEvents=true with orderBy=startTime to expand recurring events when listing
4. On 410 fullSyncRequired, drop the stored syncToken and do a full sync
5. Back off exponentially on 403 and 429 usageLimits, up to 32 or 64 seconds