What is a UUID?
A UUID is a 128-bit identifier written as 32 hexadecimal digits in an 8-4-4-4-12 pattern. Its point is that anyone can mint one without asking a central authority and still be safe from collisions, which is what makes it useful for database keys, request identifiers, and file names generated on many machines at once.
This generator produces version 4 UUIDs, which are entirely random, and version 7 UUIDs, whose first 48 bits are a millisecond timestamp so that values sort by creation time. It can also read an existing UUID and tell you its version and variant.
UUIDs are 128 bits long and are intended to guarantee uniqueness across space and time.
Features
- v4 and v7
- Version 4 is random and the usual default. Version 7 is time-ordered, which keeps database indexes compact — random keys scatter B-tree inserts across the whole index, and that cost shows up as write amplification on large tables.
- Bulk generation
- Generate 1, 5, 10, or 50 at a time and copy the whole list in one click, for seeding fixtures or filling a test table.
- Formatting options
- Uppercase and hyphen-free variants for systems that store UUIDs as a plain 32-character string.
- Inspect an existing UUID
- Paste any UUID to read its version and variant, and — for v7 — the timestamp embedded in its first six bytes.
- Cryptographically random
- Values come from the browser's crypto.randomUUID() and crypto.getRandomValues(), not Math.random(), so they are unpredictable as well as unique.
How to use
- 1
Pick a version
v4 for a plain random identifier, v7 when you want the values to sort by creation time.
- 2
Choose how many
Generate one or up to fifty at a time.
- 3
Adjust the format
Switch to uppercase or drop the hyphens if the target system stores UUIDs that way.
- 4
Copy them
Copy all copies the whole list, one per line.
Frequently asked questions
What is the difference between UUID v4 and v7?
v4 is 122 random bits, so two v4 values have no relationship to each other or to time. v7 puts a 48-bit millisecond timestamp in front of the random part, so values generated later sort after earlier ones. Use v7 when the UUID will be a primary key or will be sorted; use v4 when ordering would leak information you would rather not expose.
Can two UUIDs ever collide?
In principle yes, in practice no for v4: with 122 random bits you would need to generate roughly 2.7 × 10^18 of them before a 50% chance of a single collision. The real risk is not the mathematics but a weak random source — which is why this tool uses the browser's cryptographic generator rather than Math.random().
Is a GUID the same as a UUID?
Yes, in practice. GUID is Microsoft's name for the same 128-bit identifier. Some older Microsoft tooling prints it in braces or mixed case and uses a different byte order internally, but the value format is the same.
Should I use a UUID as a database primary key?
It is a reasonable choice when identifiers must be generated outside the database or merged across systems, but a random v4 key fragments the index because each insert lands in a different page. If that matters, use v7 — it keeps inserts sequential while remaining globally unique.
Are these UUIDs generated on a server?
No. They are generated in your browser by the Web Crypto API and never transmitted, so no one — including this site — has seen the values you copy.
Specifications this follows
- RFC 9562 — Universally Unique IDentifiers (UUIDs) — The current standard, which obsoletes RFC 4122 and introduces the time-ordered version 7.
- RFC 9562 §5.7 — UUID Version 7 — Defines the 48-bit millisecond timestamp prefix this tool reads back.
- MDN — Crypto.randomUUID() — The cryptographically secure generator used here — not Math.random().