UUID Generator
Generate cryptographically random UUID v4 in bulk. Uppercase and hyphenless options.
About this tool
A UUID is a 128-bit identifier designed to be practically unique no matter where in the world it is generated. This tool creates UUID version 4 in your browser using a cryptographically secure random source and never sends the values anywhere. Specify a count to prepare IDs or test data in bulk.
The shape and contents of a UUID
A UUID is written as hexadecimal in five groups of 8-4-4-4-12, e.g. 550e8400-e29b-41d4-a716-446655440000. That is 32 hex digits = 128 bits, a few of which are fixed bits indicating the "version" and "variant". For v4, the remaining 122 bits are random.
v4 (random) vs v7 (time-ordered)
RFC 9562, published in 2024, defines UUIDs up through v7. v4 is mostly random and scatters with no relation to creation order. v7, by contrast, starts with a millisecond timestamp, so values increase in the order they were generated. This tool outputs v4, but for cases where you want values sorted by creation time, v7 is worth considering.
Care when using them as database primary keys
Because v4 is random, using it as a primary key scatters each insert across the index, which can slow writes as row counts grow (index fragmentation). For tables with steady time-ordered inserts, a time-ordered v7 or ULID can be gentler on the index. If performance is not a concern at your scale, plain v4 is perfectly fine.
What "unique" really means
v4's random portion is 122 bits, giving roughly 5.3Γ10^36 possible values. Even by the birthday math, reaching a realistic collision probability would require an astronomical number of generations, so ordinary use never needs to worry about duplicates. If strict uniqueness is still a hard requirement, pair them with a database unique constraint.
A UUID is not a secret
v4 is hard to guess, but a UUID is still just an identifier. It often appears in URLs and logs, so avoid relying solely on "knowing the UUID means having access" (protecting something with an unguessable URL alone) and keep it alongside real authentication and authorization.
How to use
- Set the count, and optionally uppercase or hyphenless.
- Press Regenerate for new UUIDs and copy them individually or all at once.
FAQ
What is UUID v4?
A UUID whose value is mostly built from random numbers. Its high randomness makes collisions effectively unlikely, so it is widely used where a unique identifier is needed, such as database primary keys and request IDs.
How secure are the generated values?
They are generated using a cryptographically secure random source (the browser's crypto feature). Because they are harder to predict than simple pseudo-random numbers, they are more reliable as IDs.
Can I generate several at once?
Yes. Specify how many you need and generate them in a batch β handy when you want a lot of IDs for test data.
Can I get uppercase or hyphen-free forms?
Yes. Output options let you uppercase the letters or remove the hyphens, which suits file names or tokens where you do not want separator characters.
Are the generated UUIDs sent to a server?
No. Both generation and the random source run entirely in your browser (on your device), and the values are never sent externally.
Are they really guaranteed unique?
In theory the chance of a collision is not exactly zero, but the random space is so vast that in practice you can use them without worry. For systems where strict uniqueness is an absolute requirement, pairing them with a database unique constraint adds peace of mind.
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