What is an API?

API (Application Programming Interface) is a set of rules and tools that allows different software components to interact with each other. In the context of QA, API is an interface through which requests can be sent to an application and responses received, enabling automated testing without the need to work with the user interface.

For example, REST API allows sending HTTP requests (GET, POST, PUT, DELETE) to a server and receiving data in JSON or XML format to verify the correctness of the service.