An Application Programming Interface, commonly abbreviated as API, is a software interface that allows controlled access to specific functions of an application, service, operating system or data source. Through an API, two different systems can exchange information according to predefined rules and request-response structures. An API does not transfer all features of one application into another application. It allows authorised functions to be used through defined standards.
APIs are widely used in web applications, mobile applications, operating systems, databases, libraries and cloud services. For example, a website may use APIs to display cryptocurrency prices, weather data, payment services or map features. In this process, the website sends a specific request to the relevant service, and the service returns a response in an appropriate format. This allows developers to use existing services securely and consistently instead of building every function from scratch.
Flight search platforms provide a clear example of API usage. When a user selects a departure city, destination, date, passenger count and cabin class in a travel application, the system can exchange data with different airlines or travel providers. Prices, availability and flight times are retrieved from relevant providers and presented to the user in a comparative format. Platforms such as Skyscanner can combine information from many providers through these types of integrations.
APIs can differ according to their access level. An Open API, or public API, is made available to external developers under certain rules. An Internal API is used only by an organisation’s own systems and teams and is not exposed to external users. Partner APIs may also be provided to selected business partners. Each API may have different terms of use, authentication methods, rate limits and data access permissions.
APIs also play an important role in mobile devices. For example, when an application needs to use a phone’s camera, it relies on the camera API provided by the operating system. Location data, push notifications, fingerprint authentication and file access can also be handled through operating system APIs. This allows developers to use secure and standardised interfaces instead of interacting directly with device hardware.
APIs make it easier for digital products to work together through integration. Google Maps, payment systems, social login, advertising platforms, CRM tools and data analytics services can all be connected to different applications through APIs. However, API usage is not limited to creating a technical connection. Security, authorisation, data privacy, performance, error handling and sustainable integration architecture are also essential parts of proper API implementation.
