What is a UUID?
UUID (Universally Unique Identifier) is a 128-bit label used to uniquely identify objects in computer systems. The standard format is 8-4-4-4-12 hex digits separated by dashes: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx. The probability of collision with v4 is astronomically low — roughly 1 in 5.3×10³⁶.
UUID v4 vs v1 — which should I use?
v4 (random) is the safe default for database primary keys because it leaks no information. v1 is great when you need time-sortable IDs or need to trace when a record was created. v1 UUIDs embed the timestamp and MAC address.
Is UUID the same as GUID?
GUID (Globally Unique Identifier) is Microsoft's term for UUID. They follow the same RFC 4122 format. The only practical difference is presentation style: GUIDs are often wrapped in {braces} and used in .NET, SQL Server, and Windows APIs.
How unique is UUID v4?
Extremely. With 2¹²² possible values (~5.3×10³⁶), you'd need to generate 1 billion UUIDs per second for 85 years to have a 50% chance of a single collision. For all practical purposes, collisions are impossible.
What is UUID v5 and when should I use it?
v5 uses SHA-1 to hash a namespace + name into a deterministic UUID. Use v5 when you need reproducible IDs — the same input always produces the same UUID. Great for content-addressable storage or idempotent API keys.
Is it safe to generate UUIDs in the browser?
Yes. This tool uses the browser's built-in crypto.randomUUID() (for v4) and crypto.getRandomValues() (for v1/v5), which are CSPRNG-based — the same source used by password managers. No data is sent to any server.