UUID Generator

Fresh version 4 or version 7 identifiers, one or a whole batch. Generated in your browser, nothing is sent to a server.

Version

UUID v4

UUID v7

How many

Uppercase

Hyphens

Hit Generate and a fresh identifier shows up here.

Learn more about UUIDs

What is this tool?

A UUID is a 128-bit identifier. RFC 9562 defines how those bits are laid out and how to print them: 32 hexadecimal digits in five groups, separated by hyphens. Version 4 fills almost all of those bits with random data. Version 7 starts with the current Unix time in milliseconds, then random bits, so the text form sorts in creation order.

This tool draws new identifiers in your browser. It can draw one or a batch of up to 100. It does not check whether an identifier you already have is in use somewhere, and it does not store what it generates.

Typical use cases

Creating a primary key before a row is sent to a database.
Naming a file, a request id or a correlation id while debugging.
Choosing version 7 when an index should follow insertion time.
Choosing version 4 when the identifier must not reveal when it was created.

How to use it

Pick version 4 or version 7.
Choose how many identifiers you want, from 1 to 100.
Turn on uppercase or turn off hyphens only if the system that will read them requires that shape.
Press Generate. Copy one line, or copy the whole batch.

Generation runs entirely in your browser, with the Web Crypto random source. Nothing is uploaded.

Before / after examples

The values below are fixed illustrations of the layout. A real click draws fresh random bits, so you will not see these exact identifiers.

One version 4 identifier

Before

version 4, count 1, lowercase, hyphens

After

550e8400-e29b-41d4-a716-446655440000

Three version 7 identifiers from the same millisecond

Before

version 7, count 3, 2026-01-01T00:00:00.000Z

After

019b76da-a800-7000-8000-000000000000
019b76da-a800-7001-8000-000000000000
019b76da-a800-7002-8000-000000000000

In that version 7 example the random bits are zeros, so the layout is easy to read. The first 48 bits are the Unix time in milliseconds. The next group starts with the version nibble 7 , then a 12-bit counter: 000 , 001 , 002 . A real batch fills the remaining bits at random and still keeps that order.

Common mistakes

Hyphens removed when the canonical form is required

Invalid

550e8400e29b41d4a716446655440000

Valid

550e8400-e29b-41d4-a716-446655440000

RFC 9562 prints a UUID as 36 characters: eight, four, four, four and twelve hexadecimal digits, with hyphens between the groups, in lowercase. Some parsers accept the 32-digit form. Many do not. Leave the hyphens on unless you know the consumer wants them gone.

Version 4 used as a chronological sort key

Version 4

aaaaaaaa-bbbb-4ccc-8ddd-eeeeeeeeeeee
00000000-0000-4000-8000-000000000001

Version 7

019b76da-a800-7000-8000-000000000000
019b76da-a800-7001-8000-000000000000
019b76da-a800-7002-8000-000000000000

Version 4 text does not sort by creation time. The two lines above can be drawn in either order. Version 7 text sorts by the embedded timestamp, then by the counter used inside the same millisecond.

A version 7 identifier reveals when it was created. Anyone who can read it can read that time. Use version 4 when the creation time must stay hidden.

Good to know

Random bits come from crypto.getRandomValues . Version 4 uses crypto.randomUUID when the browser provides it. Both are cryptographically strong sources. Math.random is not used.
Inside one batch, version 7 keeps order in the same millisecond with a 12-bit counter in the rand_a field. That is method 1 of RFC 9562 section 6.2. If the counter would wrap, the timestamp moves forward by one millisecond.
Uppercase and hyphens change only the text. The 128 bits stay the same. The spec asks implementations to output lowercase.
One batch contains at most 100 identifiers. Changing the version or the count does not replace the list until you press Generate again.
The share link stores the identifiers that were generated, plus the options. Opening the link does not draw a new batch.
Versions 1, 3, 5, 6 and 8 are not generated. The nil UUID (all zeros) and the max UUID (all bits one) are not generated either.

Did you know?

RFC 9562 was published in May 2024 by K. Davis, B. Peabody and P. Leach. It obsoletes RFC 4122, which was published in July 2005. Version 7 is defined there, not in the older RFC.

A version 4 UUID has 122 random bits (128, minus 4 bits of version and 2 bits of variant). A collision becomes likely only around 2^61 identifiers, roughly 2.3 quintillion. That is the birthday bound, not a promise that a collision is impossible.

The 8-4-4-4-12 text form comes from earlier UUID work in the Apollo Network Computing System and OSF DCE, later written up for the IETF. Version 1 stored a timestamp counted in 100-nanosecond steps from 15 October 1582, and often a MAC address. Version 7 uses Unix milliseconds and random bits, so it does not expose a machine address.

Frequently asked questions

Does any of this leave my browser?: No. Generation uses the Web Crypto API on your machine. The page does not send the identifiers to a server. A share link puts them in the URL fragment: that fragment is not sent with the HTTP request, but anyone who has the link can read them.
Are two generated identifiers guaranteed to be different?: No generator can promise that for random identifiers. With a cryptographic random source, a version 4 collision is extraordinarily unlikely at normal volumes. Version 7 adds the current time, which makes an accidental collision with an older identifier even less likely, but it is still not a mathematical proof.
When should I use version 7 instead of version 4?: Use version 7 when the identifiers will be inserted into an ordered index and you want new rows to land near each other. Use version 4 when you want an opaque id that does not tell a reader when it was created.
Can I use one as a password or a secret token?: No. A UUID is an identifier. Version 7 publishes its creation time in clear bits. Version 4 is hard to guess, but identifiers are often written to logs, URLs and databases. A password needs a different design.