A version-4 UUID is a 128-bit identifier with 122 random bits, written as 32 hex digits in five dash-separated groups, like 550e8400-e29b-41d4-a716-446655440000. Because it is random, two independently generated v4 UUIDs are astronomically unlikely to collide, so you can mint them anywhere without coordination - which is why they are the default for primary keys, request IDs, and idempotency keys.

Are these UUIDs cryptographically random?

Yes. They are generated with the browser Web Crypto random source (crypto.randomUUID or crypto.getRandomValues), which is a cryptographically secure random number generator. That is the right source for identifiers; do not use Math.random for UUIDs, as it is predictable.

Should I use UUID or an auto-increment ID?

UUIDs let you generate an ID on the client or across services without a central counter, and they do not leak how many records exist - useful for distributed systems and public identifiers. Auto-increment integers are smaller and index more tightly. Many teams use a UUID (or a sortable variant like UUIDv7) for external IDs and keep a numeric primary key internally.

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UUID generator.

Generate cryptographically random version-4 UUIDs — one or a thousand at once, upper or lowercase, with one-click copy. The right kind of random, straight from the browser’s crypto source.

How many Uppercase No dashes

IDs you can mint anywhere

The quiet power of a UUID is that any process, on any machine, can generate one with no coordination and trust it will be unique. That is what makes them the default for request IDs you trace through logs, idempotency keys that stop a retried payment from charging twice, and primary keys in distributed systems where a central counter would be a bottleneck. Reach for the cryptographic random source, not Math.random, and a v4 UUID is effectively collision-proof.

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