An API (application programming interface) is a documented way for one software system to request data or actions from another. It defines what can be requested, how the request must be formatted, how access is authorized, and what the response or error will contain.
What happens during an API request?
- A client sends a request to an endpoint, which represents a resource or operation.
- The request includes a method, parameters or a body, and usually authentication credentials.
- The server validates the request, applies business rules, and returns a structured response.
- The client reads the status and data, then handles success, validation errors, rate limits, or temporary failures.
An API schema describes the available operations and data formats. Many HTTP APIs exchange JSON. Specifications such as OpenAPI can make this contract readable by both people and software tools.
API, user interface, and integration
A user interface is designed for a person to operate. An API is designed for software to use. An integration is the working connection built with one or more APIs, including authentication, data mapping, scheduling or events, error handling, monitoring, and maintenance.
For example, an order-management system can request new orders from a store API, translate them into its own data model, send fulfillment updates, and retry safely when a platform is temporarily unavailable. The API is the contract; the integration is the complete operational workflow.
What makes an API reliable to integrate?
- Clear documentation: endpoints, fields, examples, limits, and error definitions.
- Secure access: appropriate authentication, authorization, secret handling, and transport encryption.
- Predictable change management: versioning, deprecation notices, and migration guidance.
- Operational controls: idempotency where needed, pagination, retries with backoff, logs, and monitoring.
- Useful errors: status codes and messages that help developers correct or retry a request.
How a unified commerce API works
Commerce platforms expose different APIs, authentication models, data schemas, and version lifecycles. A unified API normalizes common commerce operations behind one interface while preserving platform-specific limits and differences that integrators still need to test.
API2Cart provides a unified API for 70+ supported shopping carts and marketplaces. See How It Works, browse Supported Platforms, or review the API technology resources before designing an integration.
