UUID Generator
Generate random version 4 UUIDs (GUIDs), one at a time or in bulk, and check what kind of UUID you have.
Version 4, RFC 9562, browser cryptographic random numbers ยท By Stuart Mathieson · Updated October 2026
Everything runs in your browser - nothing you enter is sent to a server.
What is a UUID?
A UUID (universally unique identifier) is a 128-bit value used to label things - database rows, files, messages, devices - without a central authority handing out numbers. Microsoft calls them GUIDs (globally unique identifiers); they are the same thing. A UUID is written as 32 hexadecimal digits in five groups:
The 13th digit is the version, and the first digit of the fourth group shows the variant. In a standard version 4 UUID the version is always 4 and the variant digit is 8, 9, a or b. The remaining 122 bits are random.
This generator uses your browser's crypto.randomUUID(), which draws on a cryptographically secure random number generator - the same source used for encryption keys - rather than Math.random().
UUID versions
| Version | How it is made |
|---|---|
| 1 | Timestamp plus a node ID, often the computer's MAC address |
| 3 and 5 | A hash (MD5 or SHA-1) of a namespace and a name - the same name always gives the same UUID |
| 4 | Random - the most widely used |
| 6 | Like version 1, reordered so UUIDs sort by time |
| 7 | Unix time in milliseconds followed by random bits - sorts by creation time |
| 8 | Custom layouts for vendor-specific uses |
RFC 9562, published in 2024, replaced the original RFC 4122 and added versions 6, 7 and 8. Version 7 is becoming popular for database keys because new IDs sort after older ones, which keeps indexes efficient.
Can two UUIDs be the same?
In theory yes, in practice no. With 122 random bits there are about 5.3 × 1036 possible version 4 UUIDs. By the birthday problem, you would need to generate about 2.71 quintillion (2.71 × 1018) of them for a 50% chance of a single duplicate - a billion UUIDs a second for 86 years.
That assumes a good random number generator. Problems in real systems come from poor randomness, such as copying a virtual machine with its generator's state, rather than from the maths.
Things to know
- UUIDs are identifiers, not secrets. Don't use one as a password or a security token on its own - for that, see the Password Generator.
- Uppercase and lowercase UUIDs are equal - RFC 9562 says to output lowercase, but to accept either.
- Braces
{...}are a Microsoft convention, used in the Windows registry and some .NET code. - The nil UUID (all zeros) and max UUID (all f) are special values, not random UUIDs.
Frequently asked questions
What is the difference between a UUID and a GUID?
Nothing important - GUID is Microsoft's name for a UUID. Both are 128-bit identifiers written as 32 hexadecimal digits, like 3f2b8c1e-9d4a-4f6b-8e2c-1a7d5b9c0e34.
Are version 4 UUIDs really unique?
Not guaranteed, but a duplicate is vanishingly unlikely: you would need about 2.71 quintillion random UUIDs for a 50% chance of one collision.
Should I use UUID version 4 or version 7?
Version 4 is fully random and reveals nothing. Version 7 starts with a timestamp, so IDs sort by creation time, which suits database primary keys - but it reveals when the ID was made.
Are the UUIDs generated here stored anywhere?
No. They are created by your browser's crypto.randomUUID() on your device and never sent to a server.
Sources
- RFC 9562: Universally Unique IDentifiers (UUIDs) - IETF, 2024
- Crypto: randomUUID() method - MDN Web Docs