UUID Generator — Bulk RFC 4122 v4 UUIDs
Generate random RFC 4122 version-4 UUIDs in bulk. Choose how many you need, press Generate, and copy the list — all in your browser.
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What this tool does
This tool produces random version-4 UUIDs, the standard 128-bit identifiers used in databases, APIs, distributed systems and anywhere a unique key is needed without a central counter. Each UUID is written on its own line so the output can be pasted straight into a script, a spreadsheet column or an import file. Generation happens entirely in the page; no value is ever sent to a server.
Method
A version-4 UUID is 128 bits arranged as 122 random bits plus 6 fixed bits. The
random bits come from the browser's cryptographic random number generator. Four bits in the
third group are set to 0100 to mark the version as 4, and two bits in the fourth
group are set to 10 to mark the RFC 4122 variant. The result is formatted as
8-4-4-4-12 hexadecimal digits, for example f47ac10b-58cc-4372-a567-0e02b2c3d479.
Because 122 bits are random, there are 2122 (about 5.3 × 1036) possible version-4 UUIDs. Collision risk is therefore negligible: about 100 billion UUIDs would need to be generated before the probability of a single collision approached one in a billion. This is why independent systems can mint UUIDs without coordinating and still avoid clashes.
Example
| UUID | Field | Value |
|---|---|---|
f47ac10b-58cc-4372-a567-0e02b2c3d479 | Version | 4 — the first digit of the third group |
f47ac10b-58cc-4372-a567-0e02b2c3d479 | Variant | a — the first digit of the fourth group, in 8/9/a/b |
In the sample, the third group is 4372: its leading 4 identifies the
version. The fourth group is a567: its leading a is one of
8, 9, a or b, which encode the two variant
bits 10. Every UUID this tool generates carries those same two marks.
Frequently asked questions
What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit label written as 32 hexadecimal digits in five hyphenated groups, 8-4-4-4-12. It is designed so that identifiers can be generated independently, without a central authority, and still not collide in practice. The format is defined by RFC 4122.
Is a version-4 UUID actually random?
Yes. Version 4 uses 122 random bits; the remaining 6 bits are fixed, four to mark the version and two to mark the variant. This generator fills those bits with the platform cryptographic random number generator (crypto.getRandomValues) and falls back to Math.random only when that is unavailable.
Can two generated UUIDs ever be the same?
The chance is negligible. There are 2^122 possible version-4 UUIDs, about 5.3 × 10^36. To reach a one-in-a-billion chance of any collision you would need to generate roughly 100 billion UUIDs. For any realistic list, duplicates do not occur.
Are UUIDs suitable as secrets or passwords?
No. A version-4 UUID contains about 122 bits of randomness, but UUIDs are commonly logged, stored in URLs and treated as public identifiers. If you need a secret, generate a dedicated key or token instead of reusing a UUID.
Is anything sent to a server?
No. Every UUID is generated in your browser by the page script, and the list is only written to the output box. Nothing is uploaded, logged or stored.
Can I control how many UUIDs are produced?
Yes. Set the count between 1 and 100 and press Generate. One UUID is written per line so the list can be pasted directly into a spreadsheet, a migration script or a configuration file.
Go deeper
Longer explanations of the problems this tool solves:
Sources
- RFC 4122, A Universally Unique IDentifier (UUID) URN Namespace.
Everything runs in your browser — nothing you type is uploaded.