Generate v4 UUIDs instantly — click to copy
A UUID (Universally Unique Identifier) is a 128-bit number used to identify information in computer systems. The standard representation is a string of 32 hexadecimal characters split into five groups by hyphens: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. UUIDs were designed to be generated without a central coordinating authority — any system can generate one with near-zero risk of collision with any other UUID ever generated.
Version 4 UUIDs, which this tool generates, are based on random or pseudo-random numbers. This tool uses crypto.getRandomValues() — the Web Cryptography API — for cryptographically secure randomness. Two specific bits are reserved for version information (the 4 in the third group) and variant (the first bits of the fourth group), leaving 122 bits of randomness.
The probability of two v4 UUIDs colliding is approximately 1 in 5.3 × 10³⁶. For context: if you generated one billion UUIDs per second for the next hundred years, the probability of a single collision would still be negligibly small. In practice, UUID collisions are a theoretical concern, not a practical one.
The UUID specification defines several versions, each generated differently and suited to different use cases.
| Version | Generation method | Use case |
|---|---|---|
| v1 | Timestamp + MAC address | Ordered by time; exposes network address (privacy concern) |
| v3 | MD5 hash of namespace + name | Deterministic — same input always gives same UUID |
| v4 | Random (cryptographically secure) | General-purpose unique identifiers — most widely used |
| v5 | SHA-1 hash of namespace + name | Deterministic, more secure than v3 |
| v7 | Unix timestamp + random | Time-ordered random UUIDs — better database index performance |
v4 is the default choice for most developers because it requires no external input and produces unpredictable values. v7 is gaining popularity for database primary keys because its time-ordered nature improves B-tree index efficiency at scale.
| Format | Example | Used in |
|---|---|---|
| Standard | 550e8400-e29b-41d4-a716-446655440000 | Most databases, APIs, general use |
| No hyphens | 550e8400e29b41d4a716446655440000 | Compact storage, some databases, URLs |
| UPPERCASE | 550E8400-E29B-41D4-A716-446655440000 | Some Windows APIs, legacy systems |
| Braces | {550e8400-e29b-41d4-a716-446655440000} | Microsoft COM/DCOM, Visual Studio, registry |
UUIDs are generated using crypto.getRandomValues() with the correct v4 bit masking applied (version bits set to 0100, variant bits set to 10xx). All generation happens in your browser — nothing is sent to any server. Use the bulk generator to create up to 100 UUIDs at once, then copy them all with one click.