Square

Square's API is exceptionally well-designed for commerce solutions, offering over 20 APIs with 100+ endpoints covering payments, inventory, bookings, and team management.

OAuth2 authentication is straightforward with excellent SDK support across 7 languages. The developer experience is outstanding with API Explorer, comprehensive documentation, webhooks, and robust sandbox testing. Real-time event tracking and idempotency support ensure reliable integrations. The platform excels at combining online and in-person payments with integrated hardware solutions. However, some advanced features require App Marketplace approval.

It's ideal for businesses of any size needing a complete commerce platform, particularly strong for retail and hospitality with seamless POS integration.