What is the difference between UUID v4 and v7?

v4 is 122 bits of randomness with no ordering. v7 puts a Unix millisecond timestamp in the first 48 bits and fills the rest randomly, so identifiers generated later sort after earlier ones.

Which should I use as a database primary key?

v7. Because the values increase over time, index pages fill sequentially instead of fragmenting the way random v4 keys do.

Are these random values safe?

They come from the browser's cryptographic random number generator, and everything is generated locally — nothing is transmitted or logged.

Can two people generate the same UUID?

The probability is negligible: v4 has 2^122 possible values, and v7 additionally separates identifiers by timestamp.

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UUID Generator (v4 & v7)

Generate random v4 or time-ordered v7 UUIDs, singly or in bulk.

VersionHow manyUppercaseWrap in bracesNo hyphens

7515a364-7e34-4f59-9e1e-7fe9c9175f51
b47f1c74-f162-4af1-88b9-b15374b9de13
8e67ab18-4420-4a24-8b89-4135cd359ec4
395c3663-71ec-4e56-a9b7-cacc087ab57d
a7598f7b-6456-4557-837b-77f4d4f9859b
1f7cb8d6-4e81-4a2e-918d-7b70d2b855af
06f051bf-de3b-4bea-b84d-78ebc73fb84c
3aa8794e-eda2-4da1-9d3b-3aa5f5da2914
1a15e8cc-5c48-43a9-8cc0-b6e05c2f59be
5cc0f0e0-cd70-47e7-9734-03e62996eea4

v4 vs v7, in short

UUID v4 is 122 bits of pure randomness with no ordering — great for opacity, poor for database indexes because inserts land in random places. UUID v7 puts a Unix millisecond timestamp in the leading 48 bits and fills the rest randomly, so identifiers generated later always sort after earlier ones, which keeps B-tree indexes append-mostly and far faster under heavy insert load.

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This tool is free and unrelated to what we sell. FairSoftware supplies genuine one-off Microsoft licences — Office licences and Windows licences, delivered by email.

About this tool

Generate UUIDs for databases, test fixtures, message keys or anything else that needs a unique identifier. Version 4 is fully random; version 7 embeds a millisecond timestamp in its leading bits, so identifiers sort chronologically — which keeps database indexes far happier under insert load. Generate one or thousands, with formatting options and a download.

How to use the Free UUID Generator — v4 and v7

Pick version 4 (random) or version 7 (time-ordered).
Set how many identifiers you need.
Choose formatting: uppercase, hyphens, or wrapped in braces.
Click Generate.
Copy the list to the clipboard or download it as a text file.

Frequently asked questions

What is the difference between UUID v4 and v7?: v4 is 122 bits of randomness with no ordering. v7 puts a Unix millisecond timestamp in the first 48 bits and fills the rest randomly, so identifiers generated later sort after earlier ones.
Which should I use as a database primary key?: v7. Because the values increase over time, index pages fill sequentially instead of fragmenting the way random v4 keys do.
Are these random values safe?: They come from the browser's cryptographic random number generator, and everything is generated locally — nothing is transmitted or logged.
Can two people generate the same UUID?: The probability is negligible: v4 has 2^122 possible values, and v7 additionally separates identifiers by timestamp.

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