How it works
Version 4 fills 122 bits with secure random values, so every ID is unique for practical purposes. Version 7 starts with the current Unix time in milliseconds, so IDs sort in creation order — handy as database keys. The checker reads any UUID's version, variant and, for v1 and v7, the embedded timestamp.
v4: random · v7: time + random
Which version to use
- v4: the classic choice for request IDs, filenames and anything needing an unguessable ID.
- v7: better for database primary keys, because new rows sort after old ones and indexes stay fast.
- v1: time plus MAC address — avoided here, because it leaks hardware and time information.
Tips
- Lowercase hex with dashes is the standard form; uppercase or dash-less input is still recognized by the checker.
- Never use a UUID as a password or secret — v7 embeds the time, and even v4 carries no key-stretching.
- Everything runs in your browser; nothing is uploaded.
Standards and sources
- Universally Unique IDentifiers (UUIDs): RFC 9562 (v4 random, v7 time-ordered)
Last reviewed October 12, 2026
Frequently asked questions
Should I use v4 or v7?
Use v4 for unguessable IDs such as request IDs and filenames. Use v7 for database keys, because new rows sort after old ones and keep indexes fast.
Can two UUIDs collide?
Version 4 carries 122 random bits, so generating a billion IDs per second for a century still leaves the collision chance far below one in a billion. Version 7 adds the timestamp, which separates IDs further.
What does the checker read?
The version nibble, the variant bits and, for v1 and v7, the timestamp hidden inside the ID. Dash-less or uppercase input is normalized automatically.
Can I use a UUID as a password?
No. Even v4 has no key-stretching, and v7 embeds the creation time. Use the password generator for secrets.