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What it does
Generates RFC 4122 version-4 UUIDs - 128-bit identifiers whose 122 random bits come from the browser’s CSPRNG (crypto.randomUUID, with a getRandomValues fallback that sets the version and variant bits by hand). Set how many to generate (1-1000), toggle the canonical hyphenated form against the plain 32-character form, switch hex case, then copy a single value or the whole batch. Everything is generated locally in your browser.
How to use it
- Set Count - anything from 1 to 1000; out-of-range values are clamped.
- Pick Hyphens / Plain - the canonical
8-4-4-4-12layout, or the compact form with no hyphens. - Pick Upper / Lower - the case of the hex letters. Lowercase is the RFC’s canonical form.
- Press Generate for a fresh batch. Each row has its own Copy button; Copy all puts the whole batch on the clipboard, one value per line.
- The URL captures your settings -
?n=25&upper=1&hyphens=0- so a shared link reproduces the exact configuration.
Examples
One generated
UUIDUUIDA 128-bit identifier generated to be practically unique without coordination, most commonly in version-4 (fully random) form.
in every output format (same value, three renderings):| Format | Output |
|---|---|
| Hyphenated, lowercase (canonical) | 0b944491-186e-4f18-a2f1-4d1c5c13e7a4 |
| Uppercase | 0B944491-186E-4F18-A2F1-4D1C5C13E7A4 |
| Plain | 0b944491186e4f18a2f14d1c5c13e7a4 |
The five hyphen-separated groups are not decoration - two of them carry fixed bits:
| Group | Hex chars | Value in a v4 UUIDUUIDA 128-bit identifier generated to be practically unique without coordination, most commonly in version-4 (fully random) form. |
|---|---|---|
time-low |
8 | random |
time-mid |
4 | random |
time-hi-and-version |
4 | a literal 4, then 3 random chars |
clock-seq |
4 | one of 8 9 a b, then 3 random chars |
node |
12 | random |
That is why every v4
UUIDUUIDA 128-bit identifier generated to be practically unique without coordination, most commonly in version-4 (fully random) form.
has a4 as its 13th hex digit and an 8, 9, a, or b as its 17th - you can check a claimed v4 at a glance.
Good to know
- Collision odds: a v4
UUIDUUIDA 128-bit identifier generated to be practically unique without coordination, most commonly in version-4 (fully random) form.
carries 122 random bits. You would need to generate about 2.7 x 10^18 of them before the chance of a single duplicate reaches 50%. For any realistic table, uniqueness is a certainty - and no coordination between machines is needed to claim it. - Identifier, not proof: a
UUIDUUIDA 128-bit identifier generated to be practically unique without coordination, most commonly in version-4 (fully random) form.
’s job is to distinguish a row, not to authenticate the holder. A UUID in a URL is a reference, not a permission; for bearer credentials use the Secure Token Generator. - As a database key: random keys spread inserts across the whole B-tree index. The index stays balanced, but you lose the write locality of sequential keys - at
UUIDUUIDA 128-bit identifier generated to be practically unique without coordination, most commonly in version-4 (fully random) form.
scale usually a fair trade. - Both text forms are the same 128 bits; the hyphenated one is the RFC 4122 canonical representation, and most stores accept either.
- Private: generation runs entirely in your browser through the Web Crypto API. Nothing is sent anywhere.
- Related tools:
ULIDULIDA 128-bit identifier like a UUID, but timestamp-prefixed and Crockford-base32 encoded — so it sorts by creation time and is shorter to read.
Generator, Secure Token Generator.