UUID Generator and Inspector

How to use it

1. 1Choose whether to generate identifiers or inspect oneThere is nothing to paste if you just want new UUIDs — they are generated as soon as the page loads. Switch to inspecting and a box appears for the identifier you want explained. Everything happens inside your browser — nothing is uploaded, so there is nothing for us to store, log or lose.
2. 2Read the result as it updatesThere is no button to press. Identifiers appear immediately, and change as you adjust the options. The output recomputes every time you change the text or one of the options above it.
3. 3Choose v4 or v7v4 is random and the safe default. v7 is time-ordered, which makes it far kinder to a database index — rows written in order rather than scattered — while still being unguessable enough for an identifier.
4. 4Set how many you needGenerate a batch in one go rather than reloading. They are produced with your browser's cryptographic random source, not Math.random.
5. 5Paste one in to check itThe tool reports its version and variant, and says plainly when a string is not a UUID at all. A v7 also carries its creation time, which is shown.
6. 6Copy or download the resultThe buttons under the output put it on your clipboard or save it as a file, and each one says exactly what it will copy or download. Any note about something the tool changed or deliberately left alone is shown with the result rather than hidden.

About this tool

A UUID is a 128-bit identifier that can be generated independently anywhere and still be effectively unique — no coordinating server, no central counter. This tool generates them and, given one, tells you which version it is and what it encodes.

Both version 4 and version 7 are offered because they solve different problems. Version 4 is pure randomness. Version 7 puts a millisecond timestamp in its leading bits, so values sort in creation order — which matters a great deal when the UUID is a database primary key.

Understanding the result

Every value is generated with your browser's cryptographic random number generator, never Math.random(). UUIDs routinely become session identifiers and reset tokens, and a predictable one is a vulnerability rather than an identifier.

Inspecting a UUID reports its version, its variant, and — for versions 1 and 7 — the timestamp it carries. The nil and max UUIDs are recognised as themselves rather than assigned a version they do not have.

A batch of version 7 UUIDs generated in the same millisecond still sorts correctly. That takes the monotonic counter from RFC 9562 §6.2; without it the sort order that is the whole point of v7 breaks in exactly the case where you generate several at once.

Example

Inspect: 018f8c4a-7b2e-7c31-8a4d-2f9e1b6c0d55

Version 7 — Unix time then random, sortable
Variant: RFC 9562
Created: 2024-05-06T09:14:22.510Z

Limitations

• Version 7 embeds a creation time. That is the feature, but it also means the identifier leaks when the record was made — which may not be acceptable in a public URL.
• Uniqueness is probabilistic, not guaranteed. For version 4 the probability of a collision is negligible at any realistic scale, but it is not zero.
• Versions 3 and 5, which derive a UUID from a name, are not generated here. They need a namespace and an input string and are a different task.
• A UUID is not a secret by nature. Version 4 is unguessable in practice; version 1 and version 7 are not, because part of them is a timestamp.

Questions