Toolrack

UUID Generator

Works offlineNothing is uploadedFree, no sign-up
Carries no timestamp, so it reveals nothing about when it was made
Up to 1,000 at a time
Read in your browser — nothing is sent anywhere
Version—
Variant—
Created—

Generated on your device with the browser's cryptographic RNG.

Generate UUIDs — random v4 or time-ordered v7 — one at a time or in bulk, in whichever format your system expects, and paste any UUID back in to read its version and creation time.

Anatomy of a v4 UUID

Take f47ac10b-58cc-4372-a567-0e02b2c3d479. The 4 starting the third group is the version marker, and the a starting the fourth group encodes the variant — its top bits are always 10, so that character is only ever 8, 9, a or b. Every other hex digit is random.

That leaves 122 random bits out of 128. The hyphens carry no information; they exist purely to make the value readable, which is why the no-hyphen format is just as valid and stores in 16 bytes either way.

How unlikely a collision really is

122 random bits give 5.3 × 10³⁶ possible values. The birthday bound says the count at which a collision becomes likely is roughly the square root of that, not the number itself:

UUIDs generatedChance of one collisionAt a billion per second
103 trillion1 in a billion29 hours
103 quadrillion1 in a thousand3.3 years
2.7 quintillionEven odds86 years

Which is why a duplicate in production is a bug report about the random source, not a statistical curiosity.

Which version to use

VersionBased onUse when
v1Timestamp + MAC addressLegacy — leaks hardware identity
v4RandomDefault for public identifiers
v5Namespace + name (SHA-1)Same input must give the same ID
v7Timestamp + randomDatabase keys needing sortable inserts

Frequently asked questions

When should I choose version 7 over version 4?

Whenever the identifier becomes a database key. A v4 is sixteen random bytes, so consecutive inserts land all over a B-tree and every one dirties a different page; a v7 carries a millisecond timestamp in its leading bits, so identifiers made in order sort in order and inserts stay at the end of the index. Choose v4 when the identifier is public and should reveal nothing — a v7 tells anyone holding it roughly when the record was created.

Do the v7 UUIDs generated together actually sort?

Yes. Everything in one batch shares a millisecond, so the timestamp alone cannot order them — the remaining bits would be random and the set would look sortable without being so. This generator keeps a counter in the twelve bits RFC 9562 reserves for exactly that, and steps into the next millisecond when the counter fills, so a run of a thousand comes out in the order it was made.

What is a version 4 UUID?

A 128-bit identifier where 122 bits are random and 6 are fixed markers identifying the version and variant. Because it carries no timestamp, MAC address or counter, it reveals nothing about when or where it was created — which is exactly why it is the default choice for public-facing identifiers.

Can two UUIDs collide?

In theory yes, in practice no. With 122 random bits there are 5.3 × 10³⁶ possible values, and you would need to generate roughly 2.7 quintillion of them to reach even odds of a single collision. At a billion per second that is 86 years of continuous generation. Every real-world duplicate traces back to a broken random source, not to bad luck.

Should I use a UUID as a database primary key?

It depends on the index. Random UUIDs scatter writes across a B-tree, which fragments the index and hurts insert performance at scale — a real cost in MySQL and SQL Server with clustered indexes. UUIDv7, which puts a timestamp in the high bits, keeps inserts sequential and is the better choice for new schemas that want both properties.

Are these generated securely?

Yes. They come from crypto.randomUUID() where available, falling back to crypto.getRandomValues() with the version and variant bits set correctly. Both draw from the operating system's cryptographic entropy pool, so the output is suitable for identifiers that must be unguessable, such as invite tokens.

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