FAQ
What is a UUID?
A Universally Unique Identifier is a 128-bit value, typically represented as 32
hexadecimal characters split into five groups by hyphens - e.g. 550e8400-e29b-41d4-a716-446655440000.
They are used wherever a unique identifier is needed without a central authority
assigning them.
What does v4 mean?
The version describes how the UUID was generated. v4 means it is entirely random
- 122 of the 128 bits are random, with the remaining 6 bits reserved to encode
the version and variant. Unlike v1, it encodes no timestamp, MAC address, or
other system information.
What is v7 and when should I use it?
UUIDv7 embeds the current Unix timestamp (in milliseconds) in the first 48 bits,
followed by 4 version bits, 12 random bits, 2 variant bits, and 62 more random
bits. Because the timestamp comes first, v7 UUIDs sort chronologically when
ordered lexicographically. This makes them much friendlier for database indexes
(B-trees, clustered PKs) than random v4 UUIDs, which cause fragmentation on
every insert. Use v7 when you need both uniqueness and natural ordering by
creation time - for example as primary keys in Postgres or MySQL.
Are they truly unique?
In practice, yes. With 2¹²² possible values, the probability of a collision is
negligibly small - you would need to generate about 2.7 × 10¹⁸ UUIDs before a 50%
chance of any two being identical. They are safe to use as primary keys in
databases, filenames, or any context requiring a unique identifier.
To put that in perspective: holding the Generate button produces 400 UUIDs per second. If you
wanted to re-generate a specific UUID by chance - say
550e8400-e29b-41d4-a716-446655440000 - you would need to hold it for roughly 10³⁴
seconds on average. The universe is only ~4.3 × 10¹⁷ seconds old. That is about 30 quadrillion
times the age of the universe, with the mouse button held down.
What does holding the Generate button do?
While the button is held down, new UUIDs are generated continuously at high speed
- useful if you want to pick one that "feels right" or just enjoy the animation.
Releasing the button freezes the list so you can click any entry to copy it.