The Anatomy of a UUID

A Universally Unique Identifier (UUID) is a 128-bit number used to identify information in computer systems. While it appears as a random string of characters, it is actually a strictly defined binary format containing distinct fields for time, version, variant, and randomness.

Interactive Decoder (Hover Segments)Standard: RFC 4122 (v1)
123e4567-e89b-12d3-a456-426614174000

Hover over the parts of the UUID above to identify them.

The "Variant" Field

Often overlooked, bits 64-66 define the "Variant".

  • 10xVariant 1: The RFC 4122 Standard (What we use today).
  • 110Variant 2: Microsoft GUID Legacy (pre-standard).

The "Nil" UUID

00000000-0000-0000-0000-000000000000

A special case representing "no value" or "unknown". It is filled entirely with zeros and is often used as a placeholder or default value.