UUID Generator
What a UUID is
A 128-bit identifier that can be created anywhere, by anyone, without asking a central authority whether it is taken — which is exactly why distributed systems use them. Version 4, the kind generated here, is almost entirely random.
Reading the shape
A UUID looks like xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx. The 4 is the
version, and y is always 8, 9, a or b. Everything else is random, so 122 of the 128
bits carry the uniqueness.
Where they are used
- Database keys that must be generated before the row reaches the server.
- Request and trace identifiers in logs.
- File and upload names that must not collide.
- Idempotency keys, so a retried payment is not charged twice.
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Frequently Asked Questions
In theory yes, in practice no. A v4 UUID has 122 random bits; you would need to generate billions per second for decades before a collision became likely. It is safe to treat them as unique.
From crypto.getRandomValues, the browser's cryptographic random source — the same one used for keys. Math.random is not used, because its output is predictable enough to be unsuitable.
The 4 at the start of the third group marks the version, and the first character of the fourth group is always 8, 9, a or b. Those bits identify the format, so only 122 of the 128 bits are random.
It works and removes any need for coordination between servers, but a random UUID scatters index writes and is larger than an integer. If write throughput matters, look at a time-ordered id such as UUIDv7 or ULID.
Yes. GUID is Microsoft's name for it, which is why you often see it wrapped in braces. Both are the same 128-bit value.