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UUID Standards Guide

UUID versions 1-5, format breakdown, generation examples in Python/JavaScript/Go, and when to use each version.

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UUID Format 

xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

Example: 550e8400-e29b-41d4-a716-446655440000

M = version digit (1-5)
N = variant bits (8, 9, a, or b for RFC 4122)
Total: 128 bits = 32 hex digits + 4 dashes

UUID Versions

Version Algorithm Unique by Use case
v1 Time-based MAC + timestamp Sortable, DB primary keys
v2 DCE Security MAC + POSIX UID Legacy, rarely used
v3 MD5 hash Namespace + name Deterministic, reproducible IDs
v4 Random 128-bit random General purpose (most common)
v5 SHA-1 hash Namespace + name Deterministic (preferred over v3)
v7 Unix time + random Timestamp + random Sortable, modern DBs (2023+)

Standard Namespaces (for v3/v5)

Namespace UUID
DNS 6ba7b810-9dad-11d1-80b4-00c04fd430c8
URL 6ba7b811-9dad-11d1-80b4-00c04fd430c8
OID 6ba7b812-9dad-11d1-80b4-00c04fd430c8
X.500 DN 6ba7b814-9dad-11d1-80b4-00c04fd430c8

Generation Examples 

# Python
import uuid
uuid.uuid4()           # v4 random
uuid.uuid1()           # v1 time-based
uuid.uuid5(uuid.NAMESPACE_DNS, 'example.com')  # v5

# JavaScript (browser/Node)
crypto.randomUUID()    # v4 (modern)

# Go
import "github.com/google/uuid"
uuid.New()             // v4

# SQL (PostgreSQL)
SELECT gen_random_uuid();   -- v4

When To Use Which Version

  • › v4: Default choice for most applications — simple, random, no dependencies
  • › v7: New projects needing sortable IDs (better DB index performance than v4)
  • › v5: Need same ID for same input (idempotent operations, content addressing)
  • › v1: Legacy systems requiring MAC address traceability
  • › Avoid v2/v3: v2 is rarely supported; v5 is strictly better than v3

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