UUID Generator

What a version 4 UUID is

A UUID is a 128-bit identifier written as 32 hexadecimal characters in five hyphen-separated groups, such as 3f2504e0-4f89-41d3-9a0c-0305e82c3301. Version 4 means the value is essentially all random: 122 of the 128 bits come from a random source, while the remaining bits mark the version and variant. That is why the third group always begins with a 4 and the fourth group begins with 8, 9, a or b.

Why collisions are not a practical concern

With 2¹²² possible values, you would need to generate billions of UUIDs per second for many years before a duplicate became likely. That is what makes UUIDs safe to create independently on different machines without any coordination.

Where they are used

• Database primary keys that must be generated before an insert
• Request and trace identifiers in distributed systems and logs
• File and object names in storage buckets
• Idempotency keys for payment and API requests
• Device, session and installation identifiers

Formatting choices

The canonical form is lowercase with hyphens. Uppercase and brace-wrapped forms are common in Microsoft ecosystems, and the hyphen-free form is handy when an identifier has to fit a fixed 32-character column. All three are the same value.