What kind of UUIDs does this generate?

It generates version-4 UUIDs as defined by RFC 4122 — random except for the fixed version digit (4) and the variant bits. These are the most common general-purpose identifiers and are extremely unlikely to collide across systems.

Are the UUIDs cryptographically random?

Yes. The tool uses the Web Crypto API — crypto.randomUUID where available, otherwise crypto.getRandomValues — which draws from your operating system's cryptographically secure random source rather than the predictable Math.random.

Do the generated IDs leave my browser?

No. Generation happens entirely on your device in JavaScript. No UUID is transmitted to or logged by any server, which matters when the ids will become real database keys or tokens.

What is the nil UUID option for?

The nil UUID is the all-zeros value 00000000-0000-0000-0000-000000000000. It is a valid special UUID often used as a placeholder, a default, or a sentinel meaning none. Enable the option to include it as the first entry.

Which format should I choose?

Lowercase with hyphens is the canonical RFC 4122 form and is the safe default for most databases and APIs. Use the hyphen-free form for compact storage, uppercase for systems that expect it, and the braced form for Microsoft GUID contexts and the Windows registry.

UUID Generator — Gera Tools

Generate UUIDs that will not collide

A UUID (universally unique identifier), also called a GUID, is a 128-bit value written as 32 hexadecimal digits in the familiar 8-4-4-4-12 pattern. This generator produces RFC 4122 version-4 UUIDs — the kind you reach for when you need a primary key, a request id, or a token that is safe to create independently on many machines without coordination.

How it works

A version-4 UUID is 122 random bits plus a few fixed bits. The generator fills 16 random bytes from the Web Crypto API, then sets the version nibble to 4 and the variant bits to 10xx exactly as the standard requires, and finally formats the bytes as lowercase hexadecimal with hyphens in the canonical positions. Where the browser exposes crypto.randomUUID, that native call is used directly. Either path draws from a cryptographically secure source, so the result is unpredictable and the chance of two generated UUIDs ever matching is vanishingly small.

The format options are pure presentation applied after generation: changing case, stripping hyphens, or wrapping the value in curly braces does not change the underlying random bytes.

Tips and example

A canonical UUID looks like f47ac10b-58cc-4372-a567-0e02b2c3d479 — note the 4 that marks version 4 and the a (a variant-10xx digit) right after it.
For database columns typed as uuid in PostgreSQL, keep the default lowercase hyphenated form.
Generate in bulk to seed test fixtures, then use Copy all to paste a newline-separated list into your editor.
Because generation is local and cryptographically random, these ids are safe to use as real secrets or keys.