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UUID / GUID Generator

Generate cryptographically random version-4 UUIDs in bulk for test data, primary keys, and request IDs.

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UUID v4 Output
Click "Generate UUIDs" to create some

Generate RFC 4122 version-4 UUIDs

A UUID (Universally Unique Identifier) is a 128-bit identifier designed so that generating one independently, anywhere, is astronomically unlikely to collide with any other UUID ever generated. This tool generates version-4 UUIDs — the random-based variant, and by far the most common type used in application development — using your browser's cryptographically secure random number generator (crypto.getRandomValues).

How unlikely is a collision?

A v4 UUID has 122 random bits (the other 6 bits are fixed to identify the version and variant). To have a 50% chance of a single collision, you'd need to generate roughly 2.7 quintillion UUIDs. For virtually any practical application — database primary keys, request IDs, test fixtures — collisions are not a realistic concern.

Typical use cases

  • Primary keys: Many systems use UUIDs instead of auto-incrementing integers, especially in distributed systems where IDs are generated by multiple services independently.
  • Request/trace IDs: Tag each API request with a unique ID for tracing through logs.
  • Test data & mock records: Generate a batch of realistic-looking unique IDs for fixtures or seed data.
  • Idempotency keys: Some APIs use a client-generated UUID to safely retry a request without duplicating it.

UUID vs. auto-incrementing integer: which should you use?

SituationBetter fit
Single, centrally controlled databaseAuto-incrementing integer
Multiple services generating IDs independentlyUUID
Don't want to reveal how many records existUUID
Merging data from separate databases laterUUID
Storage size / index performance is critical at huge scaleAuto-incrementing integer

For the full reasoning behind each of these, including how UUIDs are actually structured and why version 4 is the one you almost always want, see What Is a UUID and Why Does It Matter?

Frequently Asked Questions

Yes. They're generated using crypto.getRandomValues(), the Web Crypto API's cryptographically secure random number generator, rather than Math.random().
UUID v1 is based on timestamp and (historically) network card address; v3/v5 are deterministic hashes of a namespace and name; v4, generated here, is purely random. v4 is the most common choice when you just need a unique, unpredictable identifier.
Up to 500 per click, to keep the page responsive. Click generate again for another batch.
No, they're generated entirely in your browser and never transmitted.
For practical purposes, yes — GUID (Globally Unique Identifier) is Microsoft's name for essentially the same concept, and the terms are used interchangeably in most contexts.
Yes, that's actually one of their common uses — unlike a sequential integer ID, a UUID in a URL doesn't reveal how many records exist or make it easy to guess neighboring IDs by incrementing a number.