UUID v4 is a randomly generated 128-bit identifier formatted as 8-4-4-4-12 hexadecimal characters separated by hyphens (e.g. 550e8400-e29b-41d4-a716-446655440000). It is defined in RFC 9562, which replaced RFC 4122 in 2024.

How random are these UUIDs?

UUID v4 generation uses the browser's crypto.randomUUID() API, which is backed by a cryptographically secure random number generator (CSPRNG). Collisions are statistically negligible.

Are the generated UUIDs unique?

With 122 bits of randomness there are 5.3 × 10³⁶ possible UUIDs. The probability of generating the same UUID twice is astronomically low, you can treat them as globally unique in practice.

Can I use these UUIDs in production?

Yes. UUIDs generated with crypto.randomUUID() are suitable for use as database primary keys, session IDs, correlation IDs, and any other use case requiring unique identifiers.

UUID v4 generator

Generate a cryptographically random UUID version 4 (RFC 9562) instantly. Click Generate for a new UUID and copy it to your clipboard. Everything runs in your browser.

Generated UUID

VERSION

Runs entirely in your browser

How it works

UUID v4 generation uses the browser's crypto.randomUUID(), backed by the operating system's cryptographically secure random number generator. Browsers without randomUUID fall back to crypto.getRandomValues and set the version and variant bits by hand.

Processing runs in your browser

UUIDs are generated entirely in your browser. All processing happens locally in your browser tab. Our servers are not involved at any point. You can inspect this yourself in your browser's DevTools Network tab.

Technical specification

UUID version 4 (random) is defined in RFC 9562 (IETF, 2024), which replaced RFC 4122. A UUID v4 contains 122 random bits; the remaining 6 bits encode the version (4) and variant (10xx in bits 64–65). This tool uses the browser's crypto.randomUUID() method (W3C Web Cryptography API), which provides cryptographically strong randomness from the operating system's CSPRNG, equivalent to /dev/urandom on Linux or BCryptGenRandom on Windows.

Standard: RFC 9562: Universally Unique IDentifiers (UUIDs)
Random bits: 122 bits (of 128 total; 6 bits encode version/variant)
Format: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx
Collision probability: ~50% at 2.7 × 10¹⁸ UUIDs generated

Related operations

For hashing identifiers into fixed-width values, try the hash generator. To produce strong random secrets, use the password generator. For encoding identifiers for transport, see Base64.

Frequently asked questions

What is a UUID v4?: UUID v4 is a randomly generated 128-bit identifier formatted as 8-4-4-4-12 hexadecimal characters separated by hyphens (e.g. 550e8400-e29b-41d4-a716-446655440000). It is defined in RFC 9562, which replaced RFC 4122 in 2024.
How random are these UUIDs?: UUID v4 generation uses the browser's crypto.randomUUID() API, which is backed by a cryptographically secure random number generator (CSPRNG). Collisions are statistically negligible.
Are the generated UUIDs unique?: With 122 bits of randomness there are 5.3 × 10³⁶ possible UUIDs. The probability of generating the same UUID twice is astronomically low, you can treat them as globally unique in practice.
Can I use these UUIDs in production?: Yes. UUIDs generated with crypto.randomUUID() are suitable for use as database primary keys, session IDs, correlation IDs, and any other use case requiring unique identifiers.

Last reviewed September 30, 2026

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