What is an API?

API: definition and meaning

An API specifies which requests one program may send to another, in which format data is passed, and which responses come back. Think of it like a restaurant menu: you can see what you can order, but not how the kitchen works.

APIs are behind almost every digital application. When an online store processes payments through a payment provider, a website embeds a map, or a CRM passes contacts to accounting, this almost always happens through an application programming interface.

How an application programming interface works

One program—the client—sends a request to a specific API endpoint, such as “give me all open orders.” The server checks the authorization, processes the request, and returns a structured response, these days usually in the JSON data format.

To prevent just anyone from accessing data, APIs are secured, for example with API keys or the OAuth 2.0 authorization framework. Good documentation describes all endpoints, parameters, and error codes.

• REST API: the most common standard on the web, based on HTTP
• GraphQL: the client requests exactly the fields it needs
• SOAP: XML-based, common in older enterprise systems
• Webhooks: the server actively notifies other systems of events

Benefits and limitations of APIs

APIs make software combinable. Instead of copying data between programs by hand, processes run automatically and with fewer errors. At the same time, proven services—for payments, shipping, or email, for example—can be integrated rather than developed in-house.

The downside: if you use external APIs, you depend on their availability, pricing, and changes. Interfaces therefore need error handling, versioning, and monitoring—and, whenever personal data is exchanged, careful attention to data protection.

• Less manual data entry and fewer gaps between systems
• Faster development by reusing existing services
• Extensible: new systems can be connected later
• Dependence on third-party providers and their changes

Real-world example: when an API makes sense

A wholesaler maintains its products in its ERP system but also sells through a B2B online store. Without an interface, prices, inventory, and orders would have to be maintained twice. Through an API, the store syncs inventory automatically and passes orders directly to the ERP.

An API makes sense whenever several systems need the same data, when partners or customers need access to data, or when an app and a website use the same backend. Nano Concepts develops and documents interfaces like these and connects existing systems such as ERP, CRM, or payment providers.