Generate and inspect UUIDs, ULIDs, and nanoids

Frequently asked questions

Which UUID version should I use?

UUID v4 (random) is the safe default. UUID v7 starts with the time, so new IDs sort after old ones, which suits database primary keys. UUID v5 makes the same ID from the same name every time. v1 and v6 are older time-based versions. For something shorter and URL-friendly, use a ULID or a nanoid.

What's the difference between UUID, ULID, and nanoid?

A UUID is 128 bits written as 36 characters. A ULID is also 128 bits, written as 26 Crockford Base32 characters, and sorts by time. A nanoid is a random string with a length and alphabet you choose. All are practically collision-free at sensible sizes; the collision odds panel shows the numbers for your settings.

How do I decode a UUID or check if it's valid?

Open Inspect an ID and paste one or more IDs, one per line. It names the version and variant, says why an ID isn't valid, shows the time inside v1, v6, v7 and ULID (in UTC and your own time), and gives other ways to write it: no hyphens, urn:uuid:, Base64 and short Base58.

Can I convert a UUID v7 to a ULID?

Yes. Both start with a 48-bit millisecond time, so a v7 UUID can be written as a ULID with the same bits. A ULID can be written as a UUID with the same bits, or as a v7 UUID, which keeps the time and turns six random bits into the version and variant.

How do v5 and v3 name-based UUIDs work?

Pick a namespace (DNS, URL, OID, X.500, or your own UUID) and type names, one per line. Each name gives one ID, and the same namespace and name always give the same ID on any computer. v5 uses SHA-1 and v3 uses MD5; prefer v5.

Can I generate a lot of IDs at once?

Yes, up to 1,000,000. Batches over 1,000 are made in the background with a progress bar, so the page stays responsive, and you download them as one file: one per line, a JSON array, CSV, SQL INSERT statements (1,000 rows each) or a quoted list.

Can I choose the time inside a v7 UUID or ULID?

Yes. Choose “A time I choose” and set a date or Unix time in milliseconds, which is handy for backfills and tests. IDs at the same moment still sort in the order they were made.

Are these IDs cryptographically random?

Yes. Random parts come from the browser's Web Crypto API (crypto.getRandomValues), not Math.random. Custom nanoid alphabets are drawn so each character is exactly equally likely; repeated characters are used once.

Are the IDs sent anywhere?

No. Generation happens entirely in your browser. No ID is uploaded, logged or stored. The page address keeps your settings so you can bookmark a setup, but never the IDs or the names you type. It's free with no sign-up.