UUID Generator: Random Version 4 and Time-Ordered Version 7 UUIDs
Generate up to 1,000 version 4 or version 7 UUIDs at once from your browser's cryptographic random source, in lowercase, uppercase, without hyphens or in braces, and read any UUID to see its version and variant, and the timestamp of a version 7 UUID.
A UUID is a 128-bit identifier written as 32 hex digits in five groups, 8-4-4-4-12. A version 4 UUID is random apart from 6 fixed bits: the third group starts with 4 and the fourth with 8, 9, a or b. A version 7 UUID puts the creation time in its first 48 bits, so UUIDs made in different milliseconds sort by creation time. This page makes either kind in your browser.
UUIDs from this page come from your browser's cryptographic random source and are not stored or logged. They are identifiers, not secrets: do not use a UUID as a password or an access token, and remember that a version 7 UUID shows when it was created.
Version 4 UUIDs
Made in your browser with Web Crypto getRandomValues; nothing is sent or stored.
- Canonical form: 017f22e2-79b0-7cc3-98c4-dc0c0c07398f
- Variant: RFC 9562 variant (10xx)
- Version 7
- Created 2022-02-22T19:22:22.000Z (Unix 1645557742000 ms)
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About the UUID Generator
RFC 9562, published in May 2024, is the current specification for UUIDs and obsoletes RFC 4122. It defines a UUID as 16 octets, written in hex as 8-4-4-4-12. Two fields say how to read the rest: the version is the top 4 bits of octet 6, the first digit of the third group, and the variant is the top bits of octet 8, so the fourth group starts with 8, 9, a or b for the RFC's own variant. A version 4 UUID is random apart from those 6 bits, which leaves 122 random bits. A version 7 UUID starts with a 48-bit count of milliseconds since midnight 1 January 1970 UTC, leap seconds excluded, and fills the other 74 bits after the version and variant with random data, so it sorts by creation time, which suits database keys. This generator draws whole random bytes from getRandomValues in the Web Cryptography API, the kind of cryptographically secure source section 6.9 of the RFC asks for, then sets the version and variant bits. Nothing leaves your browser. The reader box takes a UUID in any common form, with or without hyphens, braces or a urn:uuid: prefix, and reports its version, its variant and, for version 7, when it was made.
Frequently asked questions
Is a GUID the same as a UUID?+
Yes: RFC 9562 says UUIDs are also known as GUIDs, the name Microsoft uses, and its GUIDs are written the same 8-4-4-4-12 way. RFC 9562 notes one difference: Microsoft's COM stores GUIDs little-endian when it saves them as bytes, so the same value can look different in binary even though the text form matches.
Should I use version 4 or version 7?+
Use version 4 when you only need an identifier nobody can guess. Use version 7 when the IDs will be keys in a database index, because each one starts with its creation time and new values land near each other in the index, which section 6.11 calls better index locality. The RFC recommends version 7 over the older time-based versions 1 and 6. Note that a version 7 UUID reveals roughly when it was made.
How do I tell which version a UUID is?+
Look at the first digit of the third group. In 017f22e2-79b0-7cc3-98c4-dc0c0c07398f, the example in RFC 9562 Appendix A.6, it is 7. Paste it into the reader box and it also shows the timestamp in the first 12 digits: 2022-02-22 at 19:22:22 UTC.
Are two version 7 UUIDs made in the same millisecond in order?+
Not necessarily with this generator. It fills all 74 bits after the timestamp with random data, the default fill in section 5.7, so two values from the same millisecond are almost certainly unique, thanks to those random bits, but can come out in either order. Section 6.2 describes counters that add ordering within a millisecond; this page does not add one.
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