UUID Generator

Generate universally unique identifiers — up to 100 at a time. Three formats are available: the familiar random UUID v4, the newer time-ordered UUID v7, and ULID, a compact sortable alternative.

All randomness comes from the operating system's cryptographically secure generator, so these are safe to use as unguessable identifiers in URLs and API responses.

How it works

A UUID is a 128-bit value written as 32 hexadecimal digits in five dash-separated groups. The point is that anyone can generate one independently, with no coordination and no central authority, and still be confident it will never collide with anyone else's.

The version you choose matters more than most people expect:

• v4 is 122 random bits. It is the default nearly everywhere, and the right choice when the identifier will be public or must be unguessable. Its weakness is that consecutive values are unrelated.
• v7 puts a millisecond timestamp in the leading bits, so identifiers sort chronologically while staying unguessable in the remainder. This matters enormously for database performance: random v4 keys scatter inserts across a B-tree index, causing page splits and index fragmentation, while v7 keys append in order. If you are using UUIDs as primary keys, prefer v7.
• ULID solves the same problem as v7 but encodes 128 bits in 26 Crockford base-32 characters instead of 36. It is shorter, case-insensitive, and avoids visually ambiguous characters, which makes it pleasant in URLs.

On collisions: the probability of two random v4 UUIDs colliding is negligible in any realistic system. You would need to generate roughly 2.7 × 10¹⁸ of them before reaching a one-in-a-billion chance of a single duplicate.

Frequently asked questions