The data interchange format commonly used in web APIs is JSON, short for JavaScript Object Notation.
JSON represents information as human-readable text, most commonly with objects containing name-value pairs and arrays containing ordered values. A web API can send a JSON response such as a user record, product list, or weather forecast, allowing programs written in different languages to exchange structured data. Although JSON originated from JavaScript syntax, it is language-independent and is supported by nearly every modern programming language.
JSON became especially widespread as interactive web applications shifted toward client-server communication in the 2000s. It is usually transmitted with the application/json media type and is lighter and easier for many developers to process than older XML-based interfaces. CSV is useful for tabular data, YAML is popular for configuration, and XML remains important in some systems, but JSON is the standard quiz answer for the format commonly used by web APIs.