All questions that are related to json in the context of Sitecore including Sitecore JSS, LayoutServices and APIs should use this tag.

JSON is an open standard file format, and data interchange format, that uses human-readable text to store and transmit data objects consisting of attribute–value pairs and array data types. It is a very common data format, with a diverse range of applications, such as serving as a replacement for XML in AJAX systems. Wikipedia