UUID / GUID Generator

A UUID (Universally Unique Identifier) is a 128-bit label used to identify information uniquely. The term GUID (Globally Unique Identifier) originally came from Microsoft’s implementation of the same standard, so in practice the two words describe the same thing — Microsoft also calls their version 4 identifiers “GUIDs”.

The version nibble — the first character of the third group — is fixed at 4 for randomly generated identifiers. The four version bits are therefore not random, and the remaining 122 bits come from a cryptographically secure random source.

The first character of the fourth group encodes the variant. A conforming version 4 UUID uses 8, 9, a or b (the binary pattern 10xx), which is exactly what the verifier checks.

Yes. With 122 random bits there is a 1 in 5.3 × 10³⁶ chance of a collision for any given pair, which is far beyond the number of identifiers the universe is likely to ever create. The generator uses the browser’s cryptographic random number generator, never Math.random().

Random v4 UUIDs work well but fragment indexes because they are not sequential. For big tables, a time-ordered identifier such as UUIDv7 or an auto-increment key usually performs better. For anything security-sensitive, always generate identifiers on the server as well.