UUID

Universally Unique Identifier (UUID) is a 128-bit long number that is used by Minecraft as a label to distinguish between separate instances.

• Hyphenated hexadecimal: The RFC 9562 standard string representation of UUID^[1]. A hexadecimal representation of the UUID, with hyphens separating the different sections into individual numbers.
  The hyphen is 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.
• Hexadecimal: The same as the hyphenated hexadecimal 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 hyphenated hexadecimal 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.
  This format is deprecated as it was used before 20w12a (1.16) and was entirely replaced by the Int-array format.
  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]

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

A player UUID is generated when the user purchases and registers a new Minecraft: Java Edition account. For Bedrock Edition, the Xbox User ID^[2] (XUID, or Xbox services ID^[3]) is used instead as the unique identifier. Users can also play Java Edition in offline mode with a specified username; the unique identifier chosen for offline mode players is UUID version 3, generated from the MD5 hash of OfflinePlayer:<username>. The community often create sites (most of which are open source) that allow people to search up a name or player UUID to get their skin, player UUID, and name, this is all done with the Mojang API.

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.

Hyphenated hexadecimal format UUIDs follow the pattern xxxxxxxx-xxxx-Axxx-Bxxx-xxxxxxxxxxxx.

(The names make sense only for version 1 and 2 UUIDs, but it has been passed onto all forms of UUIDs used.)

There are five versions of UUIDs. Versions 1 and 2 are based on current time and MAC address; versions 3 and 5 are based on hashing a string; version 4 is based on completely random generation. The "version" value occupies four bits, and is located in the UUID string format at the position indicated by an "A".

The "B" position is the variant (format) of the UUID. Depending on the specific variant, it may occupy the high 1 to 3 bits:

• 0xx is the "variant 0" of Apollo NCS 1.5, an old type of UUID.
• 10x is the "variant 1" of IETF RFC 4122 (Leach-Salz). It's referred to as "variant 2" by Java.
• 110 is the "variant 2" of old Microsoft products. It's referred to as "variant 6" by Java.
• 111 is the "reserved variant". It's referred to as "variant 7" by Java.

Minecraft uses version 4, variant 1 (RFC) UUIDs, which means that the entire number with the exception of the bits used for metadata (version and variant) is randomly generated. Java's UUID.randomUUID() function performs this exact task.

A table with the locations and values of the metadata:

• UUID Java class documentation
• Generate UUIDs in hyphenated hexadecimal format
• Convert between and generate all different formats, with the exception that the non-hyphenated hexadecimal format is only accepted as input