Tiempo, Hapio and AvailEngine
Checked against each product’s own docs on 6 October 2026.
These are the APIs that, like Tiempo, schedule bookable things rather than people’s calendars: staff, rooms, tables, courts. If you’re choosing between them, the differences are in the details: what happens to a hold when a customer leaves, whether a service can need two resources at once, and how you add the businesses on your platform.
(Recal, sometimes listed alongside them, is a unified calendar-sync API: it connects people’s Google and Outlook calendars. It belongs with the calendar APIs.)
At a glance
| Tiempo | Hapio | AvailEngine | |
|---|---|---|---|
| Bookable things | Resources with capacity | Resources with a simultaneous-booking limit | Resources (staff, tables) with party-size capacity |
| Add a business | By API: one account each | A project per tenant, made in the portal | By API, with a scoped key |
| Hold while the customer pays | Expires on its own (15 min default) | Temporary bookings, which never expire on their own | Payment holds on deposits; slot holds not documented |
| Several resources in one booking | Yes, atomic (stylist + room) | Booking groups (coach + court) | Not documented |
| “Anyone available” | Candidates in your order, chosen atomically | Random, priority or equalised selection | Returned per slot |
| Recurring bookings | Series (RRULE), edited in place | Not documented | Not documented |
| Classes with places | Sessions with seats and attendees | Simultaneous-booking limit | Not documented |
| Test and live | Separate keys and data | Separate free projects | avail_test_ / avail_live_ keys |
| Signed webhooks | Yes, retried for 3 days | Yes, retried for 24 h | Yes |
Each product’s column reflects its own documentation on the date above. See the sources at the end.
Hapio
The closest to Tiempo’s model: resources, recurring schedules with blocks, services, locations, automatic resource selection, booking groups for things like a coach and a court, and signed webhooks including reminders. It also has flexible and day-based services, React booking components and a PHP SDK, with request-based pricing per project.
Two differences matter for a payment-first checkout. Its temporary bookings occupy time but, in its own words, stay temporary “indefinitely” unless you finalise, cancel or delete them, so your app must expire them. And each tenant is a project created in Hapio’s portal, so onboarding a business isn’t an API call.
AvailEngine
Aimed at developers serving many businesses: businesses are created by API with scoped keys, and it bundles Stripe deposits, a waitlist, customer records and Google Calendar sync, at a low entry price. Its model leans towards restaurants and party sizes; its “holds” are payment authorisations rather than slot holds. Its own pages disagree on the free tier (25 or 50 bookings a month).
Where Tiempo fits
Tiempo is only scheduling, done thoroughly: holds that lapse on their own and can’t be confirmed late, atomic multi-resource and “anyone” bookings under per-resource locks, rotas and overrides, buffers, classes, series that survive clock changes, and conflicts flagged when hours change. Payments, customers and reminders stay in your platform.
Read why scheduling is harder than it looks, or try the quickstart.