What the UUID generator does
A UUID (Universally Unique Identifier) is a 128-bit identifier that can be created without a central counter and is written as 32 hex characters in an 8-4-4-4-12 pattern. It serves as a database primary key, API request ID, file name or record ID in distributed systems. The current definition is RFC 9562, which replaced RFC 4122 and added versions 6, 7 and 8.
The tool does two jobs: it generates v4 and v7 UUIDs, and it decodes any UUID you paste. The decoder reads the version and variant, shows the time inside v1, v6 and v7 in UTC and in Europe/Istanbul time, and recognises the Nil and Max UUIDs.
How to use it
- Pick a version: v4 is fully random, v7 sorts by creation time.
- Enter a count between 1 and 1,000 and press “Generate UUIDs”. New values are only created by that button.
- Changing the format re-formats the same list; it does not generate new UUIDs.
- Copy the list or download it as
uuids.txt. - Paste a UUID into the decoder; the result updates as you type. Braces, the
urn:uuid:prefix, upper case and the hyphen-free form are accepted.
Versions and formats
| Version | Contents | Note |
|---|---|---|
| v1 | 60-bit time (100 ns since 1582), clock sequence, node | The node may be a MAC address |
| v3 / v5 | MD5 / SHA-1 hash of a namespace and name | The same name always gives the same UUID |
| v4 | 122 random bits | Most common, no time information |
| v6 | v1 fields reordered to sort | Time in the most significant bits |
| v7 | 48-bit Unix milliseconds + 74 random bits | The recommended sortable version for new systems |
| v8 | Implementation-specific layout | Contents are not standardised |
Format options change only the spelling: standard lower case, upper case, 32 characters without hyphens, {…} (Windows registry and .NET) and urn:uuid:… (the RFC 9562 URN). RFC 9562 recommends writing UUIDs in lower case and reading them case-insensitively.
Generation rules and collision odds
For v4 the tool uses the browser’s crypto.randomUUID(), or crypto.getRandomValues() where that is missing; Math.random is never used. With 122 random bits you would need about 2.71 × 10^18 UUIDs to reach a 50 percent chance of a single collision; in practice duplicates come from a broken random source, not from bad luck.
In v7 the first 48 bits are the Unix time in milliseconds and the remaining 74 bits are random. When several UUIDs fall into the same millisecond the tool applies method 2 from RFC 9562 section 6.2: the random part acts as a counter and is increased by a random amount. Values generated on the same page therefore stay strictly increasing, even if the clock steps back. The benefit in database indexes is that new rows are appended at the end of the index.
Example and interpretation
The example button loads 017f22e2-79b0-7cc3-98c4-dc0c0c07398f from RFC 9562 appendix A.6 into the decoder. Result: version 7, RFC 9562 variant, time 2022-02-22T19:22:22.000Z, which is 2022-02-22 22:22:22.000 (GMT+03:00) in Istanbul. The v1 example for the same instant, c232ab00-9414-11ec-b3c8-9f6bdeced846, and the v6 example 1ec9414c-232a-6b00-b3c8-9f6bdeced846 decode to the same time and clock sequence 13256.
The lesson: v1, v6 and v7 UUIDs openly carry their creation time. Anyone who sees the ID can read when the record was created. If that must stay private, use v4.
Limits and privacy
At most 1,000 UUIDs are generated at a time. v7 ordering is guaranteed only while this page is open; across devices or tabs the order depends on their clocks. The decoder does not extract a time from v2 (DCE Security) UUIDs, because that version replaces part of the time with a local ID. Names cannot be recovered from v3/v5 hashes.
UUIDs are created on your device. A share link carries the settings only; the generated list and the value in the decoder are never added. A UUID is not an access key: even though it is hard to guess, do not use it instead of a password or session token. For secret keys the WordPress salt generator fits better, and for digests the hash generator.
Frequently asked questions
Are UUID and GUID the same thing?
Yes. GUID is the Microsoft name for the same 128-bit structure. Windows tools often use upper case and the {…} form, which the format option produces.
Should I use v4 or v7?
Use v7 when you want time-ordered primary keys in a database. Choose v4 when the ID must not reveal when it was created.
Are the generated UUIDs really unique?
There is no mathematical guarantee, but with 122 random bits the chance of a collision is negligible in practice. v7 values generated on the same page are also strictly increasing.
What are the Nil and Max UUIDs?
The Nil UUID is all zeros (00000000-0000-0000-0000-000000000000) and the Max UUID is all f. RFC 9562 reserves both for special meanings such as “no value” or a boundary; the decoder recognises both.
How can I tell a UUID’s version?
The first character of the third group is the version: …-7cc3-… is version 7. If the first character of the fourth group is 8, 9, a or b, the UUID uses the RFC 9562 variant. The decoder reads this for you.