UUID Generator
These are version 4 UUIDs — 122 random bits produced by your browser's cryptographic random number generator. They are generated locally and never transmitted, so they are safe to use as real identifiers.
Generate version 4 UUIDs — one, or up to five hundred at a time — with optional uppercase and brace formatting. Every value is produced by your own browser and never transmitted, so they are safe to use for real.
How it works
A version 4 UUID is 128 bits of which 122 are random. Six bits are fixed: four identify the version, and two identify the variant. That is why every UUID here has a 4 at the start of the third group and one of 8, 9, a or b starting the fourth.
The randomness comes from the browser's cryptographic generator rather than an ordinary pseudo-random function. That distinction matters: a predictable identifier can sometimes be guessed by an attacker, which is a real weakness in systems that use IDs as capability tokens.
Worked example
A generated value looks like 3f2504e0-4f89-41d3-9a0c-0305e82c3301. The 4 beginning the third group marks it as version 4; the 9 beginning the fourth marks the variant. Any UUID lacking those markers came from a different scheme.
Generating five hundred at once is genuinely useful when seeding a test database or building fixture data — you get a block you can paste straight into a script, with no risk of accidentally reusing the same value twice.
Common questions
What is a UUID?
A 128-bit identifier written as 32 hexadecimal characters in five hyphen-separated groups. The point is that anyone can generate one independently, without coordinating with anyone else, and still be confident it will not clash with someone else's.
What does version 4 mean?
Version 4 UUIDs are almost entirely random — 122 of the 128 bits, with the remaining six fixed to mark the version and variant. Other versions derive values from timestamps or names instead. Version 4 is the one to use unless you have a specific reason otherwise.
Could two ever be the same?
In theory yes, in practice no. With 122 random bits you would need to generate billions per second for many years before a collision became likely. It is a risk people accept in banking systems, so it is fine for most things.
Are these safe to use in production?
Yes. They come from your browser's cryptographic random number generator, not a simple pseudo-random function, so they are properly unpredictable. They are also generated locally, so nobody else has ever seen them.
Why the uppercase and braces options?
Some systems expect a particular form. Microsoft tooling often writes GUIDs in braces and uppercase, while most web and Unix contexts use plain lowercase. The value is identical either way — only the presentation differs.
Is a UUID a good database key?
It depends. UUIDs let you create records without asking a central authority for an ID, which is invaluable in distributed systems and offline-first apps. The trade-off is that random values scatter across an index, which can hurt insert performance on very large tables.