UUIDTools.com

Version 1 UUID Generator

Gregorian timestamp + clock sequence + node. Legacy time-based.

Decode
Options & format

Formatting is applied instantly in your browser. A GUID is a UUID: tick Uppercase + Braces for the Microsoft registry style.

API
http://uuidtools.com/api/generate/v1

Plain-text and JSON API docs: no key required.

About Version 1 UUIDs

A version 1 UUID combines a 60-bit timestamp counted in 100-nanosecond steps since 15 October 1582, a 14-bit clock sequence, and a 48-bit node ID that was traditionally the machine's MAC address.

To protect privacy, UUIDTools never embeds a real MAC address: the node is random with the multicast bit set, exactly as RFC 9562 section 6.10 recommends. Paste any v1 UUID into the decoder to see its timestamp.

Structure

time_low (32) | time_mid (16) | 1 + time_high (16) | variant + clock_seq (16) | node (48)

When to use it

  • Interoperating with existing systems that already use v1.

When to avoid it

  • New systems: the timestamp is scrambled across the string so v1 does not sort by time. Use v7 (or v6 to migrate v1 data).
  • Anywhere a real MAC address could leak.

Frequently asked questions

Does a v1 UUID contain my MAC address?

It can: classic implementations put the machine's MAC address in the last 12 hex digits. Ours use a random node, which is flagged by the multicast bit.