What is an Application Programming Interface (API) primarily used for in web development?

An Application Programming Interface (API) is primarily used for transferring data between systems, which includes XML and other text-based formats. In web development, APIs allow different software applications to communicate with each other by providing a set of rules and protocols for requesting and exchanging data. This functionality is fundamental for enabling interactions between the front end of a web application and its back end, or between third-party services.

By using APIs, developers can fetch data from a server without needing to expose the underlying database structure or business logic. For instance, a web application can request user information from a remote server through an API call, receive the data in a structured format like JSON or XML, and then process and display that information on the web page. This process facilitates modular design, where different parts of a web application can work independently yet cohesively through defined interfaces.

Therefore, the focus on transferring XML and other text data underscores the core purpose of APIs in web development, which emphasizes communication and data exchange rather than rendering, local storage, or hardware simulation.