What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit label used to uniquely identify information in computer systems. The standard form is defined by RFC 4122 and renders as 32 hexadecimal digits grouped by hyphens, for example:
550e8400-e29b-41d4-a716-446655440000Format & Length
A UUID is always 128 bits (16 bytes). The canonical string representation is 36 characters: 8-4-4-4-12 hex groups separated by hyphens. The 3rd group starts with the version digit, and the 4th group starts with a variant digit.
xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx
M = version (1-8)
N = variant (8, 9, a, or b for RFC 4122)Versions
- v1 — Time-based
- v3 — Namespace MD5
- v4 — Random
- v5 — Namespace SHA-1
- v6 — Reordered time
- v7 — Unix time + random
- v8 — Custom
FAQ
What does UUID stand for?
UUID stands for Universally Unique Identifier. It is also known as GUID (Globally Unique Identifier) in Microsoft ecosystems.
How long is a UUID?
A UUID is 128 bits long. In its standard hyphenated form it is 36 characters (32 hex digits + 4 hyphens). Without hyphens it is 32 characters.
Can a UUID be duplicated?
The probability of a collision is astronomically small. For v4 (random), you would need to generate about 2.71 × 10^18 UUIDs to reach a 50% chance of a single collision.
What is a UUID used for?
UUIDs are used as database primary keys, distributed system identifiers, software/hardware identifiers, API keys and anywhere a unique reference is needed without a central authority.