What is the difference between UUID v4 and v7?

v4 is 122 bits of randomness, giving unpredictable IDs with no ordering. v7 embeds a 48-bit Unix-millisecond timestamp in its leading bits, so v7 UUIDs sort chronologically, which makes them far better as database primary keys because inserts stay near the end of the index.

Are these UUIDs cryptographically random?

Yes. v4 uses the browser's crypto.randomUUID, and v7 fills its random portion with crypto.getRandomValues. Both draw from the operating system's cryptographically secure random source, so collisions are astronomically unlikely.

How does the validator know the version?

The version is encoded in a fixed nibble: the first hex digit of the third group. The variant is read from the high bits of the fourth group. For v1 and v7, the tool also decodes the embedded timestamp back into a readable date.

Can it decode the time inside a UUID?

Yes for v1 and v7. v7 stores milliseconds since 1970 directly, and v1 stores 100-nanosecond intervals since 1582 which the tool converts. v4 contains no timestamp, so no time is shown.

Is any UUID I paste uploaded?

No. Generation and validation both run in JavaScript in your browser. No UUID — generated or pasted — is ever transmitted to a server.

UUID Generator & Version Validator

A UUID (Universally Unique Identifier) is a 128-bit value, written as 32 hex digits in the 8-4-4-4-12 pattern, used to label records without a central authority. This tool generates v4 (random) and v7 (time-ordered) UUIDs and validates any UUID, decoding its version, variant, and embedded timestamp.

How it works

A UUID reserves a few bits to describe itself:

The version lives in the first hex digit of the third group (positions 13). A 4 means random; a 7 means Unix-time ordered.
The variant lives in the top bits of the fourth group and is almost always 10xx, marking an RFC 4122/9562 UUID.
For v7, the leading 48 bits hold the millisecond timestamp; for v1, the time fields hold 100-nanosecond intervals since 1582.

When generating, v4 calls crypto.randomUUID() and v7 packs Date.now() plus random bytes, setting the version and variant bits explicitly.

Tips and notes

Prefer v7 for database keys: because the timestamp leads the value, new rows insert at the end of a B-tree index instead of scattering across it, which keeps writes fast and indexes compact. Use v4 when you want IDs that reveal nothing about creation order or timing.

The validator also recognises the special Nil UUID (all zeros) and Max UUID (all f), which are reserved sentinel values rather than real version-bearing identifiers.