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Booking software APIs, and Reserve with Google

Checked against each product’s own docs on 6 October 2026.

Square Appointments, Microsoft Bookings, Acuity and SimplyBook.me are complete booking products for a business: a calendar, a booking page, payments and reminders, with an API on the side. Their APIs let you integrate with a business that already uses them, through that business’s own account and subscription.

That’s the right tool for an add-on (a marketing app for Square sellers, say). It’s the wrong foundation for your own booking platform, where you want the product, the brand and the customer relationship, and only need someone else to run the schedule. That’s Tiempo’s job.

At a glance

	Tiempo	Square	Microsoft Bookings	Acuity	SimplyBook.me
Each business needs	Nothing: you create its account	A Square seller account (writes need a paid plan)	A Microsoft 365 business subscription	An Acuity subscription	A SimplyBook.me account
Built for	Platforms you build	Square sellers	Microsoft 365 organisations	Acuity customers	Service businesses; white-label resellers
Rooms and equipment via the API	Resources	Read-only on segments	Not documented	Not documented	Listed as a feature
Double booking	Refused under a lock	Buyer-level apps can’t; seller-level apps can	Not documented	Validated unless admin	Not documented
Webhooks	Signed, every change	booking.created / updated	None for Bookings	Signed	Callback URL
Payments, reminders, booking pages	Yours	Included	Included	Included	Included

Each product’s column reflects its own documentation on the date above. See the sources at the end.

Square Bookings API

Bookings in a Square seller’s Appointments calendar, alongside Square’s payments, customers and catalogue. Writing at seller level needs the seller on a paid Appointments plan, and the API can’t create team members or make them bookable. Seller-level apps can create double bookings and bookings outside hours; buyer-level apps can’t. Choose it to build for Square sellers.

Microsoft Bookings (Graph)

Graph’s Bookings API manages booking businesses, staff, services and appointments in a Microsoft 365 tenant, with Teams meetings and group appointments. Bookings isn’t among Graph’s resources with change notifications, so there are no webhooks. Choose it inside organisations that run on Microsoft 365.

Acuity Scheduling

A mature scheduling product (now part of Squarespace) with classes, packages, payments, intake forms and signed webhooks. Its API acts on one Acuity account, or many through OAuth, each with its own subscription; staff are “calendars”. Choose it to extend businesses that use Acuity.

SimplyBook.me

A modular booking product with classes, recurring services, resources, locations, payments and a Reserve with Google integration, priced by bookings per month. It also runs a white-label programme where partners manage client accounts from one admin. Choose it if you want a ready-made booking product under your brand rather than your own.

Reserve with Google

Reserve with Google is a channel rather than a booking system: it puts a “Book” button on Search and Maps. For appointments, Google’s integrations list now offers Redirect: the button sends the customer to your platform’s booking page for that business. To join, you apply as a partner, then upload daily feeds of businesses, booking links and services, and pass a sandbox and a production review. The real-time booking-server integration is documented for other programmes, offered on a limited basis.

A platform on Tiempo qualifies the same way any booking platform does: Tiempo answers availability and places bookings behind your booking page; the partnership and feeds are yours.

Where Tiempo fits

Tiempo is for building your own booking product for many businesses, without each business subscribing to anything. It does the scheduling (resources, holds, conflicts, classes, series) and nothing your product should own. Start with the quickstart or a use-case guide.