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

50b1a4d0-88a4-4d61-88ee-b5e28b31a4ab
5cc0e241-0acc-477d-a7ae-e65dd32f3a20
ee3238e6-b62a-41aa-a068-5a7a8f789df1
44cadf22-dc0c-40a0-987e-97c202f1f4f8
84d4b7d0-92a3-4c36-8d2d-c27c3e7a6716
caf11d7e-8c55-4c10-87d5-d0e448b06192
421190c4-ae27-475a-9411-65b90cbbab97
45c9114c-2675-442d-9c8c-0678dfe2b70b
eea087d8-c2f0-46c5-8927-a4ddae3f8503
0e7e3ae9-f781-45a6-9f1a-140563bc3cf0

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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