UUID Generator

A UUID (Universally Unique Identifier) is a 128-bit identifier standardised in RFC 4122 that is statistically guaranteed to be unique without any central coordination. UUID v4 uses cryptographically random bits — this tool calls crypto.randomUUID(), which uses the browser's cryptographically secure pseudo-random number generator (CSPRNG). The probability of generating a duplicate across all UUID v4 values ever created is astronomically small.

Where UUIDs are used

UUIDs are primary keys in databases where you cannot predict the next ID (distributed systems, multi-region writes, client-side insert before server confirmation). They are used as session tokens, request trace IDs, file upload identifiers, API key prefixes, and unique identifiers for objects in event logs. Because they are generated without a server call, clients can assign IDs locally and sync to the server later.

UUID v4 vs other versions

UUID v1 encodes the current timestamp and MAC address — identifies when and where it was created but leaks machine information. UUID v3 and v5 are name-based (deterministic hashes of a name + namespace) — use these when you need the same input to always produce the same UUID. UUID v4 is fully random — use it when uniqueness is the only requirement. UUID v7 (emerging) is time-ordered random, suitable for database primary keys because it produces sequential values that index efficiently.