A UUID is a 128-bit identifier that any system can generate independently, with a vanishingly small chance of ever colliding with another one — which is why databases, APIs, files and distributed systems all use them as ID cards. This free UUID generator creates proper version 4 UUIDs, the fully random kind, using your browser’s cryptographic random number generator (the same quality of randomness your operating system provides). Generate a single ID or a bulk list of up to 500, switch between lowercase and uppercase, keep or remove the hyphens, and copy the whole list in one click. Because generation happens on your device, the UUIDs are made fresh for you and are never stored, logged or reused for anyone else.
What a version 4 UUID looks like
A UUID is written as 32 hexadecimal digits in five groups separated by hyphens: 8-4-4-4-12, like 3f50c2a8-9b1d-4e7f-a5c3-2d8e6f0b1a94. In a version 4 UUID, almost every digit is random, and the exceptions are how you can recognise the version: the first digit of the third group is always 4, and the first digit of the fourth group is always 8, 9, a or b (it encodes the variant). Those fixed bits are set for you here — the generator forces them after drawing random bytes, exactly as RFC 4122 and its successor RFC 9562 specify. Everything the tool produces, with hyphens or without, uppercase or lowercase, is the same 128-bit value in different clothing; most systems accept any of these forms, and databases often store the hyphenless one.
How likely is a collision, really?
A v4 UUID has 122 random bits, so there are about 5.3 × 10³⁶ possible values. To reach even a 50% chance of one duplicate, you would need to generate roughly 2.7 × 10¹⁸ UUIDs — at a billion per second, that is about 85 years of continuous generating. This is the entire point of the design: two servers, phones or programs that have never communicated can mint IDs for the same database table and merge their records later without a central counter, a coordination step, or (in any practical sense) a risk of overlap. When people say UUIDs are “unique in practice, not in theory,” this arithmetic is what they mean.
UUID vs GUID vs the other versions
GUID is simply Microsoft’s name for the same 128-bit standard; a GUID from this tool works anywhere a UUID does. Version 4 is the right default for almost everything, but the family has others: v1 embeds a timestamp and a machine identifier (ordered, but leaks information), v3 and v5 are hashes of a name (the same input always gives the same UUID — useful for stable IDs derived from URLs), and the newer v7 mixes a timestamp with randomness so IDs sort by creation time, which databases index efficiently. If you just need an ID nobody can predict and nothing else produces, v4 — the version generated above — is the safe, standard choice.
Frequently asked questions
Are the UUIDs from this tool really random?
Yes. They are built from the Web Crypto API’s getRandomValues in your browser, a cryptographically secure source — not from Math.random. Each click draws fresh bytes.
Can I use these UUIDs in production?
Yes — they conform to the same RFC as UUIDs from any programming library, and since they are generated locally and never stored, no one else will ever receive the same list. For IDs minted inside your own software, a library call is still the right pattern.
Why would I remove the hyphens or use uppercase?
Some systems — older databases, file-naming schemes, certain APIs and URL formats — prefer the compact 32-character form, and a few legacy tools expect uppercase. The value is identical either way.
Is there a limit to how many I can generate?
The tool makes up to 500 per click so the list stays easy to copy and check. Press Generate again for a fresh batch; there is no daily or account limit.
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