Extensible Markup Language (XML)

XML (Extensible Markup Language) is a way for programs to exchange information. It is very similar to JSON (JavaScript Object Notation).

XML was originally designed to describe documents, but has be adapted to describe anything from contacts to geographic data.

APIs use XML to describe information. A XML transmission describing me might look like:

XML is a markup language much like HTML and uses opening and closing tags to describe content. It allows computers to tell the difference between my first name and last name, for example, or any other information that it describes.

XML has long been the standard for Web Service communication, however recently it has been losing ground to JSON because it is considered more bloated and less efficient to use.

As the popularity of REST increases, JSON may continue as the preferred standard, but XML will still have a place with many older developers, because it was the original way for web services to communicate.