Which type should I use?

UUID v4 is fully random and works everywhere. UUID v7 and ULID start with the creation time, so they sort in order, which keeps database indexes fast.

Can two generated IDs collide?

In practice, no. A v4 UUID has 122 random bits; you would need billions of IDs per second for decades before a collision became likely.

UUID and ULID generator: free, private, in your browser

How to use UUID and ULID generator

Pick UUID v4, UUID v7 or ULID.
Choose how many, up to 1,000.
Select Generate, then copy them or download a text file.
To see when a v7 UUID or ULID was made, paste it into the lookup box.

UUID v4, UUID v7 or ULID

UUID v4 is 122 bits of randomness in the familiar 8-4-4-4-12 format. It's the safe default and every database and language understands it. UUID v7, standardised in RFC 9562 in 2024, puts the creation time in milliseconds at the front, followed by randomness, so new IDs sort after older ones. That keeps database indexes compact and makes rows easy to order by creation.

ULID gives the same time-ordering in a shorter, 26-character string using Crockford's Base32 alphabet, which avoids letters that look alike, such as I, L and O. It suits URLs and filenames.

Secure randomness

Every ID is built from crypto.getRandomValues, the browser's cryptographic random number generator. Tools that use Math.random produce IDs that can be predicted, which matters if an ID is ever used to protect anything, such as an unlisted link. Generate up to 1,000 at once and download them as a text file, one per line.

Reading a timestamp

Because v7 UUIDs and ULIDs carry their creation time, you can read it back. Paste one into the lookup box to see exactly when it was generated, which helps when tracing a record through logs. Random v4 UUIDs carry no time, and the tool says so. Paste an ID from your logs or database to try it.

Privacy

IDs are generated in your browser and never sent anywhere, so nobody else has a copy of the IDs you use. There is no server log of what was generated, and nothing is saved between visits.

Examples

A v4 UUID looks like 3f2a9c1e-5b7d-4e8a-9c21-7d4e5f6a8b90; the 4 at the start of the third group marks the version. A v7 UUID such as 0192797a-3e4f-7c1a-9b2e-5d6f7a8b9c0d starts with its creation time, and the 7 marks the version. A ULID such as 01J9Z3K7Q8R5T2V4W6X8Y0Z1A2 is 26 characters, and its first 10 encode the time. All three are 128-bit values, so each fits the same database column type.

Questions

Which type should I use?: UUID v4 is fully random and works everywhere. UUID v7 and ULID start with the creation time, so they sort in order, which keeps database indexes fast.
Are they really random?: Yes. They use crypto.getRandomValues, the browser's cryptographic random number generator, never Math.random.
Can two generated IDs collide?: In practice, no. A v4 UUID has 122 random bits; you would need billions of IDs per second for decades before a collision became likely.