What is a UUID and what does version 4 mean?
A UUID (universally unique identifier) is a 128-bit value usually written as 32 hexadecimal digits in five groups separated by hyphens, such as 8-4-4-4-12 characters. The aim is to let separate systems create identifiers on their own without coordinating, with a negligible chance of two of them ever matching.
There are several versions. Version 4, the one this tool generates, is built from random numbers rather than a timestamp or a machine address. A few fixed bits mark it as version 4 and the rest are random. Because nothing in it reveals when or where it was made, version 4 is a common default for general-purpose identifiers.
When do you need to generate UUIDs yourself?
Most applications generate UUIDs in code, but there are plenty of times a quick batch by hand is handy. You might need sample primary keys for a database seed file, placeholder IDs for a test fixture or an API mock, a unique value for a configuration entry, or a correlation ID to tag a log trail while debugging.
A UUID is also useful when you want an identifier that does not leak information, unlike an auto-incrementing number that reveals how many records exist. If you need a secret rather than an identifier, a password generator is the better fit, because a UUID is meant to be unique, not to be kept confidential.
How to generate UUIDs with this tool
- Set the "How many?" number. The field accepts values from 1 to 100, and it starts at 5.
- Tick the Uppercase checkbox if you want capital letters. Leave it off for the usual lowercase form.
- Click Generate to create a fresh list. Five UUIDs are already shown when the page loads, but changing the number does not create new ones until you press the button.
- Click Copy all to copy the whole list to your clipboard, one UUID per line.
The list scrolls if it is long. The uppercase option changes how the values are displayed and copied, not the underlying identifiers.
Randomness, uniqueness, and limits
The UUIDs are created by your browser's built-in secure random generator, so they are produced locally and not requested from a server. The chance of a collision between random version 4 values is extremely small in practice, but the tool cannot check your database, so it does not guarantee a value is unused in your system. Keep a unique constraint on the column as a safeguard.
This tool only produces version 4. If you need time-ordered identifiers, which index more efficiently in some databases, or name-based UUIDs, you will need a different method. Also remember that regenerating replaces the list, so copy what you need before pressing Generate again.