Universally unique identifier

UUIDs (Universally Unique IDentifiers) are 128 bit long numbers which are used by Minecraft to distinguish between separate instances.

Representation

 * String: A hexadecimal representation of the UUID, with hyphens separating the different sections into individual numbers. The hyphen are set to split the UUID into numbers of the format  with each number marking the number of hexadecimal digits fitting into the corresponding section. An example of this representation would be.
 * Because every part is evaluated as an individual number, empty digits at the start of a section can be ignored. For example,   can be evaluated as the same as.
 * String without hyphens: The same as the regular String representation, but without the separation of the different sections. An example for this representation would be, where it is impossible for the majority of empty digits to be removed as opposed to the regular String representation.
 * Most/Least: A separation of the 64 most significant bits from the 64 least significant bits. Each of the two numbers is stored separately and uses the  data type in the game. An example of this representation would be   paired with.
 * int-array: A separation into four 32 bit numbers. Each part is stored in an integer array ordered from most significant to least significant. An example of this representation would be

Occurences
The following table represents the situations in which UUIDs are used in places accessible by a player:

Technical aspects
Minecraft uses variant 4 UUIDs, which means that the entire number with the exception of a few bits is randomly generated.