UUID Generator

1. 1Choose the UUID version you need.
2. 2Set how many to generate.
3. 3Pick a format: standard hyphenated, uppercase, braced, or no hyphens.
4. 4Copy the list, or download it as a text file.

A UUID is a 128-bit identifier that can be created independently anywhere without coordination, and still be unique in practice. Version 4 fills 122 of those bits with cryptographic randomness — enough that generating a billion a second for a century still leaves the chance of a collision negligible.

Version 7 solves a real problem with version 4. Random UUIDs arrive at a database in random order, which scatters writes across a B-tree index and fragments it badly. Version 7 puts a 48-bit millisecond timestamp at the front, so identifiers generated later sort later. Inserts land at the end of the index, and range queries by time become possible.

The trade-off is that version 7 leaks approximately when the identifier was created. For an internal primary key that is usually fine; for a public unguessable token, version 4 is the safer choice.

Both versions set the version and variant bits correctly, so the output validates against RFC 9562.

Reading the structure of a UUID

1. 0189d5f2-1e4c-7a3b-9c2d-4e5f6a7b8c9d
2. The 13th character is the version — 7 here.
3. The 17th character encodes the variant, always 8, 9, a or b.

Result: A valid RFC 9562 version 7 UUID whose first 48 bits are a timestamp.

• Use version 7 for database primary keys; it keeps inserts in order and indexes compact.
• Use version 4 for anything that must not reveal when it was created, such as public tokens.
• Store UUIDs in a native UUID column where your database has one; it takes less space than text.
• Use lower case in the standard hyphenated form unless a system needs something else.

• What is a UUID — and should you use version 4 or version 7?
• UUID vs auto-increment ID: which primary key to use