UUID Inspector

Decoding a UUID you were handed

Not every UUID is the random kind. An inspector validates the format, then reads the version and variant bits to tell you how it was generated, and for time-based versions it can extract the embedded timestamp. That is useful when debugging: the version alone tells you whether an id is random, time-ordered, or derived from a name.

Where the version and variant live

In the canonical form, the first digit of the third group is the version, and the first bits of the fourth group encode the variant. Version 4 is random, version 1 is time-and-MAC based, version 3 and 5 are namespace hashes (MD5 and SHA-1 respectively), and newer version 7 is time-ordered and sortable. The variant for standard UUIDs makes that fourth-group digit one of 8, 9, a, or b.

Example

c232ab00-9414-11ec-b3c8-9e6bdeced846
         ^              ^
       version 1    variant (8/9/a/b)

v1 timestamp -> 2022-02-22 19:22:22 UTC

A version-1 UUID packs a 60-bit timestamp counting 100-nanosecond intervals since 15 October 1582, which the inspector converts into a normal date. Random v4 values carry no such information. To mint new ones, use the UUID generator.

Privacy note on v1

Version 1 historically embeds the generating machine's MAC address and a timestamp, which can leak when and roughly where an id was created. If you see v1 UUIDs in a public API, that exposure is worth noting; random v4 or v7 avoids it.

FAQ

Is the nil UUID valid? The all-zero UUID is a defined special value, not a bug. It typically means unset or none rather than a real generated id.

Can I get a creation time from a v4? No. v4 is pure randomness with no timestamp. Only v1, v6, and v7 carry extractable time.