What next?
Unique identifiers, then the things that carry and verify them.
How to use this tool
- Choose how many UUIDs you need.
- Version 4 (random) UUIDs generate instantly.
- Copy them for database keys or IDs.
What your result means
Each UUID is a 128-bit identifier generated at random, with 122 of those bits truly random in a version 4 UUID. No central registry issues them and no lookup is performed — uniqueness comes from the sheer size of the number space, not from coordination.
The practical consequence is that you can generate identifiers independently on a laptop, a phone and a server and treat collisions as impossible: you would need to generate about 2.7 × 10¹⁸ UUIDs before reaching a one-in-a-billion chance of a repeat. Note the trade-off, though — v4 UUIDs are random, so they carry no timestamp and sort in no meaningful order. If you need identifiers that sort chronologically, UUID v7 or a database sequence is the better tool.
Why this one is different
The source of the randomness is named rather than assumed, and every batch is checked for repeats after minting. The first identifier appears braced, upper-cased, hyphen-free and as a URN, because registries, database columns and XML schemas each insist on a different one of those shapes, and its five groups are labelled with the bits they carry.
Unique without asking anyone
A UUID is a 128-bit identifier that's random enough to be treated as globally unique — no central authority needed. Two machines on opposite sides of the world can each mint one and be safe in the knowledge they'll never collide.
Version 4 UUIDs are almost entirely random. With about 3.4 × 10³⁸ possibilities, you could generate a billion a second for a century and never repeat one — which is why they're everywhere in databases and APIs.
Related tools
What makes a UUID unique
A version 4 UUID is 128 bits, of which 122 are random — the other six identify the version and variant. That gives roughly 5.3 × 10³⁶ possible values. The practical consequence is that you can generate identifiers independently on thousands of machines, with no coordination between them, and never realistically collide: you would need to generate about 2.7 × 10¹⁸ UUIDs before reaching a one-in-a-billion chance of a single duplicate.
Worked example
The anatomy of a version 4 UUID:
8-4-4-4-12 hexadecimal digits, 36 characters with hyphens
The 4 at the start of the third group is the version marker, and the a beginning the fourth group is the variant. Those six bits are fixed, which is why a v4 UUID carries 122 random bits rather than 128 — still enough that generating a billion a second for a century leaves the chance of a collision negligible.
Frequently asked questions
Are UUIDs guaranteed to be unique?＋
Not guaranteed in the mathematical sense — but the probability of a collision is so small that it is not a practical engineering concern, provided the generator uses a cryptographically strong random source. This tool uses the browser's crypto API rather than Math.random.
Which UUID version should I use?＋
Version 4 (random) is the right default for most applications. Version 7, standardised in RFC 9562, embeds a timestamp so that IDs sort chronologically — useful as a database primary key, because purely random keys scatter writes across an index.
Can a UUID be used as a secret or a security token?＋
A version 4 UUID from a cryptographic source has 122 bits of entropy, which is ample. But UUIDs are often logged, shown in URLs and shared casually, so treat them as identifiers rather than credentials.
What is UUIDv7 and why is it useful?＋
It puts a millisecond timestamp in the high bits, so generated values sort chronologically. That makes them far friendlier as database primary keys than random v4 values, which scatter writes across an index.
Should I use a UUID or an auto-incrementing ID?＋
UUIDs let independent systems create IDs without coordinating, and they do not leak how many records exist. Integers are smaller and faster to index. Many systems use an integer key internally and a UUID externally.
Are the UUIDs generated on my device?＋
Yes. Values come from the browser's cryptographic random source and are never transmitted, so nothing you generate here is known to anyone else.
Further reading
Assumptions & limitations
Generation is standards-compliant; the guarantees people expect from it often are not:
- Uniqueness is probabilistic, not guaranteed. Collisions are vanishingly unlikely at any realistic volume but are not impossible.
- A UUID is not a secret. Version 4 values come from a cryptographic source, but a UUID in a URL is still a public identifier.
- Version 1 and version 7 values embed a timestamp, so they reveal when the record was created.
- Random UUIDs scatter database index writes. Use version 7 where insertion order matters for performance.