What is a UUID — universal unique identifier
What is a UUID (GUID): a 128-bit identifier, versions v1–v7, and why APIs and databases use it.
A UUID (Universally Unique Identifier) is a 128-bit identifier that looks like 32 hexadecimal digits split by hyphens: 8-4-4-4-12. For example: 550e8400-e29b-41d4-a716-446655440000. Its key value is uniqueness without coordination between systems.
The Version field (fourth block) shows the generation method: v4 — random bits, v7 — creation time in the high bits, v1 — time and MAC address, v3/v5 — a hash of a name. Pick a version by the task: random IDs for entities, time-ordered for database indexes.
UUIDs are widely used in APIs, databases, and distributed systems instead of auto-increment IDs. In ToolsHelper you can generate any version and inspect an existing identifier to see its structure and time.
A UUID is 128 bits written as 8-4-4-4-12 hex digits. The version nibble says how it was built: 4 is random, 7 is time-ordered, 1 is a MAC address plus a clock. The variant nibble marks the layout. This page is the family name. Generating a v4 or a v7 is a converter, and the comparison page is which one to store.
FAQ
UUID vs GUID?
Same idea; different ecosystem jargon — GUID is a Microsoft term.
Which UUID should I pick?
Use v4 for simple entities. Use v7 when you need insert-time sortability.