This is a simple online tool for generating globally unique ids (GUIDs) aka universally unique ids (UUIDs).
On Linux, you can use the uuidgen program, but you can't always use Linux, or somehow it isn't installed, so an online tools can come in handy.
Currently it is using the randomUUID() function in the java.util.UUID class.
You can use this page as REST web service by passing in the appropriate parameters. For example https://www.fileformat.info/tool/guid.htm?count=1&format=text will return a single GUID as plain text. See the HTML source of the form for all the parameters.