UUID Generator

About UUIDs

Which version should I use — v4, v7, or v5?

v4 (random) is the safe general-purpose default: 122 random bits, no structure to read anything into. v7 encodes the current millisecond timestamp in its first 48 bits, so later UUIDs sort after earlier ones — that matters as a database primary key, since a naturally increasing key keeps B-tree inserts append-only instead of scattering writes across random pages the way v4 does, which is why Postgres, MySQL, and most ORMs have been adding v7 support. v5 is deterministic: the same namespace + name always produces the same UUID, useful for turning an existing identifier (a URL, an email, a file path) into a stable UUID without a lookup table. Because it's deterministic, the Count field doesn't apply to v5 — instead, paste one name per line to batch-convert a whole list into their UUIDs.

What are the Nil and Max UUIDs?

Reserved constants defined by the UUID spec (RFC 9562): Nil is all zero bits (00000000-0000-0000-0000-000000000000), Max is all one bits (ffffffff-ffff-ffff-ffff-ffffffffffff). Both are explicit sentinel values — "no id" or "highest possible id" — rather than identifiers anything should actually be assigned, e.g. as a database column default or an open-ended range boundary.

How unlikely is a collision, really?

A v4 UUID has 122 random bits (6 of the 128 are fixed to mark version and variant). You'd need to generate around 2.71 quintillion of them before the odds of any collision anywhere reach 50% — generating a billion a second for a hundred years doesn't get close. Generation here uses crypto.getRandomValues(), the browser's cryptographically strong random source, not Math.random().

Does this check whether a UUID is already in use somewhere?

No — there's no central UUID registry to check against, which is the entire point of the format: uniqueness comes from the math (enough random bits, or a namespace+name hash), not from coordinating with a database. Inspect only tells you what a UUID's own bits say about it (version, variant), not where else it might appear.

Does this tool upload my data anywhere?

No. Generation and inspection both happen entirely in your browser via the Web Crypto API. Nothing is sent anywhere, which also makes it safe to inspect real UUIDs pulled from your own systems here.