Generate version 4 (random) UUIDs — the exact type this tool produces.
Version 4 UUIDs are 128-bit identifiers generated from random or pseudo-random numbers, formatted as 32 hex digits split into five groups (8-4-4-4-12). They are the default choice for database primary keys, request IDs, and idempotency keys where you need a value that is unique for all practical purposes without a central coordinator handing out numbers.
This tool uses your browser’s built-in crypto.randomUUID(), which is cryptographically random — the same quality of randomness used for security-sensitive values — rather than a weaker Math.random()-based generator. Generate one UUID or up to 500 at once for seeding test data.
The chance of two v4 UUIDs colliding is astronomically small (roughly 1 in 2.7 x 10^18 for any two given values), which is why they are treated as unique without needing to check a database.
Worked example: in a generated UUID like 3fcc84cc-d4c4-4301-a9ef-936a55651c73, only 122 of the 128 bits are actually random — the rest are fixed markers that identify the UUID's type. The first character of the third group is always "4" (here, in "4301"), marking this as version 4. The first character of the fourth group is always 8, 9, a, or b (here, "a" in "a9ef") — a variant marker required by the UUID specification. Those 6 fixed bits are why the earlier collision-probability figure is based on 2^122 possibilities, not the full 2^128 the raw bit-length would suggest.
Not mathematically guaranteed, but the collision probability is so small (about 1 in 2.7 quintillion for two random v4 UUIDs) that they are treated as unique in practice.
Version 4 — the randomly-generated variant, as opposed to v1 (timestamp-based) or v5 (name-based hashing).
Yes, that is one of the most common uses, though be aware v4 UUIDs are not sequential, which can affect index performance on very large tables compared to sequential IDs.