UUID Generator
Generate random v4 UUIDs instantly. Single or batch generation, copy to clipboard. Free, browser-based, no server required.
- Runs in your browser
- Your data never leaves your browser
- Free · No Sign-Up
Scan with WeChat to share this tool
Examples, details and FAQ Worked examples, how it compares with other tools, and answers to common questions.
Reading a Generated UUID
One value from the tool, d4b151b4-c1d3-41ac-9d4c-d413b112aaa1, broken down by RFC 9562 sections 4.1 and 4.2:
| Part | Value | Meaning |
|---|---|---|
| 13th hex digit | 4 | Version 4: random |
| 17th hex digit | 9 (binary 1001) | The first two bits, 10, mark the RFC 9562 variant; the other two are random |
| Remaining 30 digits | d4b151b4 c1d3 1ac d4c d413b112aaa1 | Random bits: 122 in total with the two low bits of the 17th digit |
The same reading with carets under the two fixed digits; the third line gives the 17th digit in binary:
d4b151b4-c1d3-41ac-9d4c-d413b112aaa1
^ ^
4 9 = 1001A batch of three looks like this in the output box, and Copy All copies it with line breaks between the values:
656b9dfc-22b8-43d1-8615-e0f9cf5e92ce83fdc7b8-86f1-4f54-930f-02717eee5825e16f5c6d-6645-42f4-9d38-80dffe9d0245
Check any value from another source the same way: if the 13th digit is not 4, it is not a version 4 UUID. A 7
there means version 7, and a 1 means version 1, which embeds a timestamp and, in older implementations, the machine’s MAC address.
Every generated batch line follows the same v4 version and RFC variant pattern as the single value above.
How Unlikely Is a Collision?
With 122 random bits there are 2122 (about 5.3 × 1036) possible values. By the birthday bound, you need about 2.7 × 1018 UUIDs before the chance of any two matching reaches 50%. At one billion UUIDs per second, that takes about 86 years. In practice, duplicates come from bugs such as a copied seed or a value reused by mistake, not from the random bits.
After 103 trillion UUIDs the chance of any duplicate is still about one in a billion: p ≈ 1.0 × 10^-9, from p = 1 − e−n²/(2 × 2122) with n = 1.03 × 1014.
Choosing Between UUID Versions and Other IDs
- v4 (this tool): random, no information about when or where it was made. Good for public identifiers and tokens that must not reveal order.
- v7 (RFC 9562 section 5.7): 48-bit Unix millisecond timestamp, then random bits. The same section says implementations SHOULD use v7 instead of v1 and v6 where possible. The ULID Generator makes a similar time-sorted 128-bit ID in 26 characters.
- Shorter IDs: the Nano ID Generator makes 21-character URL-safe IDs with about the same amount of randomness.
Limitations
- Version 4 only. There are no options for uppercase, no hyphens, braces or URN form (
urn:uuid:…); edit the copied text if your system needs one of these. - At most 100 per batch.
crypto.randomUUID()is available in Chrome and Edge 92+, Firefox 95+ and Safari 15.4+ (MDN browser compatibility data). In older browsers the tool shows no UUID.- The tool generates values; it does not validate or decode a UUID you paste.
FAQ
What is a UUID?
A UUID (Universally Unique Identifier, RFC 9562) is a 128-bit value written as 32 hex digits in five groups. A version 4 UUID fills 122 of those bits with random data, so two independently generated values practically never match.
Are these UUIDs truly random?
They come from crypto.randomUUID(), part of the Web Crypto API, which draws from the browser's cryptographically secure random number generator. Math.random() is not used.
What is the format of a UUID?
xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx: the 13th hex digit is always 4 (the version) and the 17th, y, is 8, 9, a or b (the RFC 9562 variant). Every other digit is random. The tool writes lowercase; RFC 9562 section 4 allows upper, lower or mixed case, so readers must accept all three.
How many UUIDs can I generate at once?
Up to 100 per batch. A count above 100 is treated as 100, below 1 as 1, and an empty or non-numeric count as 5. The count is remembered in this browser; the UUIDs themselves are not stored.
Should I use UUID v4 or v7 as a database key?
v7 starts with a millisecond timestamp, so new keys sort after old ones and B-tree indexes stay compact. v4 is fully random, which spreads inserts across the index but reveals nothing about creation time. This tool generates v4 only.
Are the generated UUIDs sent anywhere or saved?
No. crypto.randomUUID() runs in this browser tab, and the values are not sent to ZeroTool or kept after you leave the page. The page saves only the batch count, in this browser's local storage. Google Analytics on the page records that Generate or Generate Batch was clicked, without the UUID values.