UUID v4 Generator

Generate one or many random UUID v4 identifiers with cryptographic randomness.

How to use

  1. Choose how many UUIDs you need (up to 100 at a time) and the formatting options.
  2. Click "Generate" — each identifier is created with the browser's cryptographic random generator.
  3. Copy the list with one click. Each UUID is on its own line, ready to paste into code, fixtures or a database.

About this tool

A UUID (Universally Unique Identifier) is a 128-bit identifier designed so that anyone can generate one at any time without coordinating with anyone else — and still be practically certain it is unique. Version 4, generated here, fills 122 of those bits with random data: the number of possible values is so large (about 5.3 undecillion) that the chance of two random UUIDs colliding is negligible for any real-world system.

UUIDs are the standard answer whenever distributed systems need identifiers without a central counter: database keys, API request IDs, file names, session tokens for non-secret purposes. The canonical format is 32 hexadecimal digits in five hyphen-separated groups (8-4-4-4-12), where the version digit is always 4 and the variant digit is 8, 9, a or b.

This generator uses crypto.randomUUID when the browser provides it, falling back to crypto.getRandomValues with the version and variant bits set manually — both cryptographically secure sources. Generation is entirely local: the identifiers are created on your device and never transmitted.

The formula

UUID v4 layout: xxxxxxxx-xxxx-4xxx-Nxxx-xxxxxxxxxxxx, where x is a random hexadecimal digit and N is one of 8, 9, a or b (the variant). 122 random bits give 2¹²² ≈ 5.3 × 10³⁶ possible values.

Frequently asked questions

Can two generated UUIDs collide?

In theory yes, in practice no. With 122 random bits, you would need to generate about 2.7 × 10¹⁸ UUIDs to reach a 50% chance of a single collision.

What is the difference between UUID and GUID?

None in practice — GUID is Microsoft's name for the same 128-bit identifier. The formats are interchangeable.

Are these UUIDs safe to use as database keys?

Yes. UUID v4 keys avoid the coordination problem of sequential IDs. Note that random keys can fragment clustered indexes — some databases prefer time-ordered variants (v7) for high-volume tables.

Is the UUID generated on a server?

No. Generation runs in JavaScript on your device with the browser's cryptographic generator. Nothing is transmitted.

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