Generate RFC 4122 version 4 UUIDs locally, with collision-probability maths for your volume.
A version 4 UUID is 128 bits, of which 122 are random: four bits encode the version and two encode the RFC 4122 variant. That leaves an identifier space of 2^122 ≈ 5.3 × 10^36 values, which is why v4 UUIDs can be generated independently on many machines without coordination. The chance that any two collide follows the birthday approximation, p ≈ n² / (2 × 2^122) for n identifiers, so even at a billion IDs the probability stays around 10^-19 — far below the failure rate of the hardware storing them. Generation here happens entirely in your browser using WebCrypto, so no identifier is ever transmitted.
Collision probability (birthday approximation)
p ≈ n² / (2 × 2^122)
Canonical v4 layout
xxxxxxxx-xxxx-4xxx-Nxxx-xxxxxxxxxxxx where N ∈ {8, 9, a, b}
Yes for uniqueness, but consider the storage and index-locality cost: a random v4 UUID scatters inserts across a B-tree index, which is why time-ordered variants such as UUIDv7 or ULID are often preferred for high-insert-rate tables.
Only when it comes from a cryptographically strong source, which this tool reports. 122 random bits is ample entropy, but many UUID libraries historically used weak PRNGs, so verify the generator rather than assuming the format implies strength.
RFC 4122 reserves the first nibble of the third group for the version number, so a version 4 (random) UUID always shows a literal 4 there. The first character of the fourth group is the variant and is always 8, 9, a or b.
At one billion UUIDs the probability is roughly 10^-19. You would need to generate about 2.7 × 10^18 UUIDs before reaching a 50% chance of a single collision.