UUID Generator
Generate random version-4 UUIDs (GUIDs) in your browser — one or up to 50 at a time, with uppercase and no-hyphen options.
Each UUID uses 122 random bits from your browser’s cryptographic RNG (crypto.randomUUID).
A UUID (Universally Unique Identifier), also called a GUID, is a 128-bit label written as 32 hexadecimal digits in the pattern 8-4-4-4-12, such as f47ac10b-58cc-4372-a567-0e02b2c3d479. This tool makes version-4 UUIDs, where 122 of the 128 bits are random, so two generated values practically never collide.
How a UUID is structured
Every UUID is 128 bits shown as 32 hexadecimal digits split into five groups by hyphens: 8-4-4-4-12. That layout — for example f47ac10b-58cc-4372-a567-0e02b2c3d479 — is fixed across all versions. Two positions are reserved: the first digit of the third group encodes the version (a 4 here), and the first digit of the fourth group encodes the variant (one of 8, 9, a, or b). The remaining 122 bits of a version-4 UUID are filled with random data.
Because 122 random bits give roughly 5.3 × 10³⁶ possibilities, the odds of two independently generated v4 UUIDs matching are astronomically small — you would need to generate billions per second for many years before a single collision became likely. That is why v4 UUIDs are widely used as database keys, request IDs, and file names without any central coordinator handing them out.
UUID versions and what they are based on
This tool generates version-4 (random) UUIDs. All versions share the 8-4-4-4-12 layout.
| Version | Based on | Notes |
|---|---|---|
| v1 | Timestamp + MAC address | Time-ordered, but can leak the machine’s MAC and creation time. |
| v3 | MD5 hash of a name + namespace | Deterministic — the same name always yields the same UUID. |
| v4 | Random (or pseudo-random) bits | This tool. 122 random bits; no inputs, no ordering. |
| v5 | SHA-1 hash of a name + namespace | Like v3 but with SHA-1; preferred over v3 for name-based IDs. |
When to reach for v4 (and when not to)
Version 4 is the right default when you just need a unique identifier and do not care about ordering or reproducibility — session tokens, message IDs, and object keys are classic uses. If you need IDs that sort by creation time, look at v1 or the newer time-ordered v7. If you need the same input to always map to the same UUID, use the name-based v3 or v5 instead. Note that a UUID is an identifier, not a secret: it is unique, but it is not a substitute for a password or an unguessable security token.