Universally unique identifier

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

Representation

Hyphenated 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 8-4-4-4-12 with each number marking the number of hexadecimal digits fitting into the corresponding section. Further detail follows in the Technical aspects section.
An example of this representation would be f81d4fae-7dec-11d0-a765-00a0c91e6bf6.
- Because every part is evaluated as an individual number, empty digits at the start of a section can be ignored.
  For example, 00000001-0002-0003-0004-000000000005 can be evaluated as the same as 1-2-3-4-5.
String: The same as the hyphenated string representation, but without the separation of the different sections.
An example for this representation would be 00000001000200030004000000000005, 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 Long data type in the game.
An example of this representation would be UUIDMost:-568210367123287600 paired with UUIDLeast:-6384696206158828554.
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 [I;-132296786,2112623056,-1486552928,-920753162]

Occurences

The following table represents the situations in which UUIDs are used in places accessible by a player:‌^{[upcoming: JE 1.16]}

Location (general)	Location (path)	Format	Use
All entities (NBT)	`UUID`	int-array	Own UUID
Attribute modifiers (NBT)	`UUID`	int-array	Own UUID. Used when equipping and unequipping the item to identify which modifier to add or remove from the entity.
Attribute modifiers (Loot table)	`id`	String	Set UUID of modifier in `set_attributes` function
Tameable mobs (NBT)	`Owner`	int-array	Owner
Projectiles (NBT)	`Owner`	int-array	Entity that shot the projectile
Item entities (NBT)	`Owner`	int-array	Target player for `/give` command
Item entities (NBT)	`Thrower`	int-array	Player who dropped the item
Shulker bullets (NBT)	`Target`	int-array	Entity targeted for attack
Conduits (NBT)	`Target`	int-array	Entity targeted for attack
Player heads (NBT)	`SkullOwner.Id`	int-array	Owner of the skin
Player heads (NBT)	`SkullOwner.Properties.textures[].Value.ProfileId`	String without hyphens	Owner of the skin
Mobs (NBT)	`Leash.UUID`	int-array	Entity that leashed the mob
Breedable mobs (NBT)	`LoveCause`	int-array	Player who fed the mob
Zombie Villagers (NBT)	`ConversionPlayer`	int-array	Player who is converting the Zombie Villager
Bees and Zombified Piglins (NBT)	`HurtBy`	int-array	Entity that hurt the bee or Zombified Piglin
Villagers (NBT)	`Gossips[].Target`	int-array	Player who caused the gossip
Target selectors (Commands)	-	String	Selected entity

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Technical aspects

Value range

A UUID can be expressed as a 128 bit number, which means that it supports all integer values from -(2^127) to (2^127)-1. It is important to note that this evaluation does not refer to the range of values generated by the game but instead focuses on the capacity of the format.

String format section names

String format UUIDs follow the pattern aaaaaaaa-bbbb-cccc-ddee-ffffffffffff.

Section name	Used symbol	Bit range
		From	To	Size
time-low	`a`	96	127	32
time-mid	`b`	80	95	16
time-high-and-version	`c`	54	79	16
clock-seq-and-reserved	`d`	36	53	8
clock-seq-low	`e`	48	45	8
node	`f`	0	47	48

Generation

Minecraft uses variant 4 UUIDs, which means that the entire number with the exception of the bits used for metadata is randomly generated.

A table with the locations and values of the metadata:

Bitwise version

[edit]

Collapsed version