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

23fce520-0b8a-46bc-8288-f8ab06c2b580
11f2dc60-592b-4d9d-9212-503849721641
555960e6-4cdb-4cc0-a944-13224815c5cc
bbc91167-11e5-4c1b-b013-77f725b33d41
1a348f17-6f68-456c-a33d-d333030907b9
74da5503-3389-430a-990f-5d85db8fd8e7
aa732047-a70e-4ace-a054-a1653b19ba9d
20062529-ba12-4837-9e0b-d2a693d3b3a9
ccbbd7b4-d9b3-4f51-9789-e889ec9387b2
99f3b896-65d8-4935-ac5a-29474702e6df

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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