UUID Generator

Version 4 (random) UUIDs from the browser's cryptographic RNG. Generate one or a thousand. Copy any single one or the whole list.

How many?

Reference UUIDs

Nil

00000000-0000-0000-0000-000000000000

Max

ffffffff-ffff-ffff-ffff-ffffffffffff

The nil UUID is the "absent" / "no-value" sentinel. The max UUID was added in RFC 9562 as its complement. Both have special semantic meaning — don't use them as actual identifiers.

What is a UUID?

30-second version

A UUID (Universally Unique Identifier, also called GUID on Windows) is a 128-bit value that — generated correctly — is astronomically unlikely to collide with any other UUID, anywhere, ever. It's a way to mint identifiers without coordinating with a central authority.

The versions you'll meet

v1 — based on timestamp + MAC address. Identifies which machine generated it and roughly when. Privacy concern if you leak it.
v3 / v5 — derived deterministically from a namespace + name via MD5 / SHA-1. Same input always produces the same UUID.
v4 — fully random (122 bits of randomness, 6 bits for version/variant). This is the one this tool generates and the one most systems use.
v6 / v7 / v8 — newer, timestamp-prefixed for sortability. v7 is increasingly popular for database primary keys.

How unique is v4 really?

With 122 random bits, you'd need to generate ~2.7 quintillion UUIDs before having a 50% chance of one collision. For comparison, every grain of sand on Earth could have a unique UUID with room to spare.

When NOT to use v4

As database primary keys at scale. Random UUIDs scatter writes across B-tree indexes, killing insert performance. Use UUID v7 (time-ordered) or BIGINT.
As secret tokens. UUIDs reveal that they're UUIDs. A secret should be opaque bytes, ideally Base64URL.
In URLs you want short. 36 characters is a lot. Consider KSUID or nanoid.