UUID & Random Number Generator
Generate UUID v4 identifiers in bulk, or draw random numbers for testing, giveaways and games. Uses your browser’s cryptographically secure random source — nothing is sent to a server.
UUID v4
Random numbers
What Is a UUID?
A UUID (Universally Unique Identifier), also called a GUID, is a 128-bit value written as 36 characters — for example f47ac10b-58cc-4372-a567-0e02b2c3d479. Its purpose is to let separate systems create identifiers independently, with no central coordination, and still never collide.
That is why UUIDs appear everywhere: database primary keys, file names, API request IDs, session tokens and message queues. Two offline devices can each mint one and stay safely unique when they later sync.
Are UUIDs Really Unique?
Version 4 UUIDs are random: 122 of the 128 bits are random, the rest identify the version. That gives about 5.3 x 1036 possibilities. To reach even a one-in-a-billion chance of a single collision you would need to generate around a hundred billion of them. In practice, collisions do not happen.
This matters only if the randomness is good. This tool uses crypto.randomUUID() where available and otherwise crypto.getRandomValues() — both cryptographically secure. Generators built on Math.random() are predictable and should never be used for anything security-related.
Fair Random Numbers
The random number section also uses the secure source, with modulo bias rejection: the naive random % range trick makes low numbers slightly more likely, so values landing in the uneven tail are discarded and redrawn. Every number in your range therefore has an equal chance — which matters if you are drawing prizes.
Tick No repeats to draw without replacement, like pulling numbered balls from a bag rather than rolling a die repeatedly.
UUID vs Auto-Increment IDs
- UUIDs can be created anywhere without asking the database, and leak nothing about how many records you hold.
- Sequential IDs are smaller, sort naturally and index more efficiently — but they reveal volume and are guessable in URLs.
- A common compromise is a sequential internal key plus a UUID for anything exposed publicly.
Frequently Asked Questions
Are these UUIDs generated on a server?
No. They are created in your browser and never transmitted, so nobody else ever sees them — including us.
Can I use a UUID as a password or secret token?
A v4 UUID carries 122 bits of entropy, which is plenty in principle. It is fine for unguessable URLs and API request IDs, but for passwords use a dedicated generator, and for session tokens use your framework’s own mechanism.
What is the difference between a UUID and a GUID?
Nothing meaningful. GUID is Microsoft’s name for the same 128-bit identifier, sometimes written in braces and uppercase, which is why both formats are offered here.
How many can I generate at once?
Up to 1,000 per click. Generation is instant because it happens locally, so repeat as often as you need.