Square

Platform for accepting payments, managing inventory, and running a business. Combines point-of-sale hardware and software with an API-first developer layer for payments, orders, customers, and commerce workflows across in-person and online channels.

Square operates under Block and is the U.S. market leader in point-of-sale systems, serving millions of sellers and processing hundreds of billions in volume annually. The developer platform exposes 20+ APIs and 100+ endpoints, with backend SDKs for Python, Node.js, Ruby, PHP, Java, .NET, and Go. An app marketplace and partner program let third-party apps extend the platform.

Key capabilities:

• Payments API, Web Payments SDK, Terminal API, and Mobile Payments SDK for online, in-person, and in-app transactions
• Orders, Catalog, Inventory, and Customers APIs for commerce and CRM workflows
• Bookings API, Loyalty API, and Gift Cards API for appointments and customer engagement
• Invoices API, Subscriptions API, and Checkout API for recurring and invoiced sales
• Webhooks, event logs, and API logs for diagnostics and real-time integrations
• Square App Marketplace for third-party integrations and custom solutions

Food and beverage sellers, retailers, beauty and wellness businesses, and service providers use Square to take payments, manage teams, and control cash flow. Developers embed Square into custom kiosks, booking systems, and omnichannel checkout flows via REST and GraphQL, with Postman collections and API Explorer for testing.