What is a UUID?
A UUID (Universally Unique Identifier, called a GUID in Microsoft tools) is a 128-bit ID written as 32 hexadecimal digits in five groups, for example 919108f7-52d1-4320-9bac-f847db4148a8. Any program can create one without asking a central server, and two randomly generated UUIDs are practically never the same.
v4 or v7?
- v4 is 122 random bits. Use it when the ID should reveal nothing, such as public IDs, file names or invitation codes.
- v7 starts with a millisecond timestamp, so newer IDs sort after older ones. As a database primary key it keeps new rows at the end of the index, which is faster than random v4 keys.
How to use
- Choose the version and how many UUIDs you need (up to 1,000).
- Turn on uppercase, remove the hyphens or add braces if your system expects that format. The list updates immediately.
- Copy the list or download it as a text file, one UUID per line.
- To check an existing UUID, paste it into "Validate a UUID" to see its version, variant and, for v1, v6 and v7, the time stored inside it.
Example
This v7 UUID comes from RFC 9562, the UUID standard:
017f22e2-79b0-7cc3-98c4-dc0c0c07398f
Its first 12 digits, 017f22e279b0, are a Unix timestamp in milliseconds. The validator shows it as:
2022-02-22T19:22:22.000Z
FAQ
Are these UUIDs random enough for production?
Yes. The random part comes from crypto.getRandomValues, the browser's cryptographically secure generator, the same quality server libraries use. The UUIDs are created in your browser and never sent anywhere.
Can two UUIDs ever be the same?
In theory, yes; in practice, no. A v4 UUID has 2122 possible values: you would need to create about a billion per second for 85 years to reach a 50% chance of a single duplicate. v7 also includes the time, so IDs created in different milliseconds can never collide.
Does a v7 UUID reveal when it was created?
Yes. Anyone can read the creation time from a v7 UUID, as the example above shows. If the creation time is sensitive, use v4.
Uppercase or lowercase?
The standard recommends lowercase output and case-insensitive comparison, so lowercase is the safest choice. Use uppercase or braces only when a system requires it, for example some Microsoft tools that display GUIDs as {...}.