UUID version 4 is the most widely used UUID type. It is generated almost entirely from random (or pseudo-random) data, which makes it ideal whenever you need a unique identifier and do not want it to leak any information about when or where it was created.
This generator creates standards-compliant v4 UUIDs entirely in your browser. Nothing is sent to a server, so it is fast, private, and works offline once the page has loaded.
What is a UUID v4?
A v4 UUID is a 128-bit value with 122 bits of randomness; the remaining 6 bits are fixed to encode the version (4) and variant. It is written as 32 hexadecimal digits in the familiar 8-4-4-4-12 pattern, for example 9b2e4f1a-3c6d-4e58-9f0a-1b2c3d4e5f60.
Because the random space is so large (2^122 possibilities), the chance of generating the same v4 UUID twice is negligible for virtually every application, even across many independent machines generating IDs at the same time.
When should you use UUID v4?
Reach for v4 when you need unguessable, collision-resistant identifiers and do not require them to be ordered or derived from a name. Common uses include database primary keys, API resource IDs, session and request identifiers, file names, and idempotency keys.
If you need identifiers that sort by creation time (for better database index locality), consider UUID v7 or ULID instead. If you need deterministic IDs derived from a name, use UUID v5.
Frequently asked questions
- Are UUID v4 values unique?
- They are practically unique. With 122 random bits the probability of a collision is around 1 in 2^122, which is so small it can be ignored for almost all real-world systems.
- Is UUID v4 secure enough to use as a secret token?
- No. While v4 UUIDs are hard to guess, they are not guaranteed to be generated with a cryptographically secure random source in every environment. Use a dedicated secure token for secrets.
- What is the difference between UUID v4 and a GUID?
- They are effectively identical. GUID is Microsoft’s name for the same 128-bit identifier; a randomly generated GUID is a UUID v4.