UUID v4
Random UUID based on random bytes (RFC 4122).
UUID v7
Time-ordered UUID with millisecond precision (RFC 9562).
What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit identifier written as 32 hexadecimal digits in five hyphen-separated groups, for example 3f2504e0-4f89-41d3-9a0c-0305e82c3301. UUIDs are designed to be unique without a central registry β different machines, services and databases can generate IDs independently and still never collide in practice.
Version 4 UUIDs are built from random bits, so 122 of the 128 bits are effectively random. Version 7, standardised in RFC 9562, embeds a Unix millisecond timestamp in the leading bits, so identifiers sort by creation time while staying globally unique β a great fit for database primary keys. Concretely, in 3f2504e0-4f89-41d3-9a0c-0305e82c3301 the 13th hex digit (4) names version 4 and the 17th (9) fixes the RFC 4122 variant.
How to use the UUID generator
- Pick a version: UUID v4 for pure randomness, or UUID v7 for time-ordered, sortable IDs.
- Click Generate to create a new identifier β generate as many as you need.
- Click Copy to put the UUID on your clipboard instantly.
- Use Clear to reset the result, and switch between v4 and v7 from the version pages.
Frequently asked questions about UUIDs
Should I use UUID v4 or v7?
Use v7 when the IDs will be database keys: because the prefix is a timestamp, inserts stay near the end of the index and avoid the page fragmentation caused by random v4 values. Use v4 when you simply need a random, opaque identifier and ordering does not matter.
Are UUIDs really unique?
For v4 the chance of a collision is negligible β you would have to generate roughly 2.7 x 10^18 UUIDs before reaching a 50% chance of one duplicate. For v7, uniqueness within the same millisecond is guaranteed by a random counter.
Can UUIDs be used as secrets?
No. UUID v4 is unpredictable, but it is not a cryptographically strong secret. Use a proper random token generator (at least 128 bits from a CSPRNG) for API keys, sessions and password-reset links.
Are these UUIDs generated on your server?
No. The generator uses the browser's crypto.getRandomValues() secure random source, so identifiers are produced on your device and are never transmitted or logged.
What is the difference between GUID and UUID?
They are the same thing. GUID (Globally Unique Identifier) is Microsoft's name for the UUID format; both use the same 128-bit structure defined in RFC 4122 and RFC 9562.
