Generate reproducible UUID v4 and v7 values from a seed, or validate any UUID or GUID and decode its version, variant and embedded timestamp.
By AdminDrafted with AI writing toolsUpdated Checked examples: 8
017f22e2-79b0-7cc3-98c4-dc0c0c07398f is a version 7 (Unix Epoch time-based) UUID with the RFC 9562 variant; it was stamped at 2022-02-22 19:22:22.000 UTC.
Lower-case hex in 8-4-4-4-12 groups: 017f22e2-79b0-7cc3-98c4-dc0c0c07398f.
Leading bits 10 mean the RFC 9562 layout; 0, 110 and 111 are reserved for older or future schemes.
This layout leaves 74 bits for random data.
A UUID is a 128-bit identifier written as 32 hex digits in 8-4-4-4-12 groups. RFC 9562 fixes two fields in every standard UUID: the variant bits 10 at the start of the 17th hex digit, and a 4-bit version number in the 13th. The decoder reads both, then unpacks what that version carries: a 48-bit Unix millisecond timestamp for version 7, a 60-bit count of 100-nanosecond intervals since 15 October 1582 for versions 1 and 6, or 122 random bits for version 4.
The default is the RFC 9562 version 7 example, 017f22e2-79b0-7cc3-98c4-dc0c0c07398f, whose first 48 bits count 1,645,557,742,000 ms, which is 22 February 2022 at 19:22:22 UTC. Developers pick v7 for database keys because the values sort by creation time.
Generated UUIDs come from a seeded xoshiro256** generator, so the same seed always gives the same list. For identifiers that must be unguessable, use a cryptographic source such as crypto.randomUUID().
A UUID is 128 bits written as 32 hex digits in 8-4-4-4-12 groups. The 13th digit is the version and the 17th carries the variant. In 017f22e2-79b0-7cc3-98c4-dc0c0c07398f the 7 marks version 7, the 9 the standard variant, and the first 12 digits count Unix milliseconds: 2022-02-22 19:22:22 UTC.
017f22e279b0.The Unix timestamp converter does step 3. The 48-bit field runs out in the year 10889.
RFC 9562 defines the current layouts and replaced RFC 4122 in 2024.
Check the variant before trusting the version digit. Standard UUIDs have 8, 9, a or b as the 17th digit. A c or d there marks Microsoft's reserved variant, where the 13th digit is not an RFC version.
The RFC's version 1 example, c232ab00-9414-11ec-b3c8-9f6bdeced846, and its version 6 twin, 1ec9414c-232a-6b00-b3c8-9f6bdeced846, hold the same instant. Both decode to 2022-02-22 19:22:22.0000000 UTC, with clock sequence 13256 and node 9f:6b:de:ce:d8:46.
Version 1 stores the low 32 time bits first, so its text sorts by the fastest-changing part of the clock. Version 6 stores the same 60 bits in order, 1ec9414c232ab00, which is why it sorts. Seven fractional digits keep the 100-nanosecond resolution.
| Scenario | Version | Embedded UTC time |
|---|---|---|
| Default | 7 | 2022-02-22 19:22:22.000 UTC |
| RFC v1 | 1 | 2022-02-22 19:22:22.0000000 UTC |
| RFC v4 | 4 | — |
| RFC v6 | 6 | 2022-02-22 19:22:22.0000000 UTC |
| Seeded v7 | 7 | 2026-01-15 12:00:00.000 UTC |
Default is the RFC's version 7 example from the first section. The RFC v4 example, 919108f7-52d1-4320-9bac-f847db4148a8, carries no time at all.
Seeded v7 is the first UUID generated from seed 42 at 2026-01-15 12:00 UTC: 019bc186-de00-7716-a104-d9866d113a7e.
Use version 4 when an ID must reveal nothing. Use version 7 for database primary keys: new values land at the end of a B-tree index instead of at random positions, at the cost of exposing each record's creation time to anyone who sees the ID.
Generated UUIDs here come from xoshiro256**, seeded through SplitMix64 (reference code), so the same seed always gives the same list. That suits fixtures and documentation.
They are predictable by design, so never use them as session IDs, tokens or production keys. For those, use a cryptographic source such as crypto.randomUUID().
All version 7 UUIDs in one list share the millisecond you choose. Their order inside that millisecond is random; RFC 9562 section 6.2 describes counters for strictly increasing IDs.
c or d variant digit follows a different layout.urn:uuid: prefix.To inspect a timestamp field in another base, use the number base converter.
Checked against: RFC 9562 Appendix A.6 (Tuesday, February 22, 2022 2:22:22.00 PM GMT-05:00)
Checked against: RFC 9562 Appendix A.3
Checked against: RFC 9562 Appendix A.1;.clock_seq = 13256;.node = 0x9f6bdeced846
Checked against: RFC 9562 Appendix A.5 (same instant as the v1 example)
Version 4 fills 122 of the 128 bits with random data, so values are spread evenly and reveal nothing. Version 7, defined in RFC 9562 (May 2024), puts a 48-bit Unix millisecond timestamp first and 74 random bits after it, so new IDs sort in creation order. RFC 9562 notes that v4 has poor database-index locality, which is why v7 suits primary keys, at the cost of revealing when each ID was made.
In practice, no. A v4 UUID has 122 random bits, so by the birthday bound you would need about 2.7 × 10^18 of them for a 50% chance of a single duplicate, or about 103 trillion for a one-in-a-billion chance. Real collisions come from faulty random number generators or reused seeds, which is why the seeded UUIDs here shouldn't be used where uniqueness across systems matters.
They are the same 128-bit format; GUID is Microsoft's name for it. Microsoft tools often print GUIDs in upper case inside braces, such as {017F22E2-79B0-7CC3-98C4-DC0C0C07398F}, and RFC 9562 allows upper, lower or mixed case, so parsers should accept both. The one real difference is binary byte order: Windows stores the first three groups little-endian, which matters only when reading raw bytes.
Take the first 12 hex digits, which hold a 48-bit count of milliseconds since 1970-01-01 00:00 UTC, and convert them to decimal. For 017f22e2-79b0-7cc3-98c4-dc0c0c07398f, 017f22e279b0 is 1,645,557,742,000 ms, which is 2022-02-22 19:22:22.000 UTC. The 48-bit field runs out in the year 10889, so it will not wrap in practice.
It can be. Version 1 stores a 60-bit timestamp and a 48-bit node field that is traditionally the machine's MAC address, so the ID reveals when and on which network card it was made; the RFC 9562 v1 example decodes to 2022-02-22 19:22:22 UTC with node 9f:6b:de:ce:d8:46. RFC 9562 allows a random node value instead, and says to use version 7 instead of 1 or 6 where possible.
This calculator includes 8 worked examples with independently sourced answers. They run in the test suite, and you can run them here too.