Free · crypto-random · in-browser
UUID Generator
Generate version 4 UUIDs using your browser's cryptographic random source — never a server, never logged. Pick the format your platform expects and copy them out.
Short answer
A UUID v4 is a 128-bit identifier written as 8-4-4-4-12 hex digits, with 122 random bits — unique without any central coordination. UUID and GUID mean the same thing; Microsoft just uses the other name. Generate one or a thousand below — crypto-random, in your browser, never sent anywhere.
Version 4 (random), from your browser's cryptographic generator.
Generated on your device — never transmitted, stored, or logged.
Related
UUID formats and where they're used
| Format | Example | Typical use |
|---|---|---|
| Standard (lowercase) | 65ede5e8-f463-4049-9b26-4bc5f11519f3 | APIs, JSON, Postgres, most languages |
| Uppercase | 65EDE5E8-F463-4049-9B26-4BC5F11519F3 | Some Microsoft tooling and logs |
| Braced | {65ede5e8-f463-4049-9b26-4bc5f11519f3} | Windows registry, .NET GUID.ToString("B") |
| No hyphens | 65ede5e8f46340499b264bc5f11519f3 | Compact storage, URL slugs, some databases |
All four spell the same 128-bit value — the format is presentation only. Examples are freshly generated, so they change on every deploy.
Why UUIDs instead of 1, 2, 3?
Sequential IDs need a single authority to hand them out — fine for one database, painful the moment you have several, an offline mobile client, or records created before they are saved. UUIDs remove the coordination entirely: any machine can mint one and be confident nobody else will produce the same value. The costs are real too — they are bulky in URLs, bigger as index keys, and unsortable in v4 form, which is why time-ordered variants like v7 exist for high-volume database keys.
How we calculate this
Version 4 UUIDs are 122 random bits with 6 bits reserved:
- Cryptographic randomness. values come from crypto.randomUUID() (or crypto.getRandomValues as a fallback) — never Math.random(), whose weak distribution would undermine the collision guarantee.
- Version and variant bits. the 13th hex digit is fixed to '4' (version) and the 17th to 8, 9, a or b (RFC 4122 variant) — which is why every v4 UUID has that shape.
- Collision odds. with 2^122 possibilities, you would need to generate roughly a billion UUIDs per second for 85 years to reach a 50% chance of a single duplicate.
Assumptions
- Generation is local: no UUID is transmitted, stored or logged, so values are safe to use as secrets-adjacent identifiers.
- Batches are capped at 1,000 to keep the browser responsive — larger sets belong in your database.
- v4 UUIDs are random, not sortable. If you need time-ordered identifiers, look at UUID v7 or ULIDs instead.
Last reviewed: July 30, 2026
Frequently asked questions
What is a UUID?+
A Universally Unique Identifier: a 128-bit value written as 32 hex digits in the 8-4-4-4-12 pattern, like 123e4567-e89b-12d3-a456-426614174000. Its point is that anyone, anywhere, can generate one without coordinating with anyone else and still expect it to be unique — which is why distributed systems use them instead of sequential IDs.
What's the difference between a UUID and a GUID?+
Nothing, in practice. GUID (Globally Unique Identifier) is Microsoft's name for the same 128-bit standard; UUID is the RFC 4122 name used everywhere else. The only visible differences are formatting habits — Microsoft tooling often wraps them in braces and uses uppercase, both of which you can toggle above.
Can two UUIDs ever be the same?+
Theoretically yes, practically no. Version 4 UUIDs carry 122 random bits — about 5.3 × 10^36 possibilities. You would need to generate a billion per second for roughly 85 years to reach even a 50% chance of one collision. The real-world risk isn't the math, it's a broken random source, which is why this tool uses your browser's cryptographic generator rather than Math.random().
Is UUID v4 secure enough to use as a token?+
The randomness is cryptographic, so a v4 UUID is unguessable in practice — but it was designed for uniqueness, not secrecy, and it's often logged, sent in URLs, or exposed in APIs. For session tokens, password resets and anything security-critical, use a purpose-built secret of at least 128 bits from a dedicated library, and keep UUIDs for identifying things.
Should I use UUID v4 or v7?+
v4 is pure random — perfect when you just need an identifier. v7 embeds a timestamp so values sort chronologically, which dramatically improves database index locality on large tables (random v4 keys scatter writes across the B-tree). If you're generating primary keys for a big Postgres or MySQL table, v7 is usually the better modern choice; for everything else, v4 is fine.
Are these UUIDs generated on your server?+
No — they're generated in your browser with crypto.randomUUID(), never transmitted, never logged, and gone when you close the tab. You can verify it in the network tab: generating a thousand UUIDs produces zero requests.
Generated with your browser's cryptographic random source — never transmitted, stored, or logged.