What is the difference between UUID v4 and ULID?

UUID v4 is 128 bits of randomness formatted as 36 characters, with no inherent order. ULID is 26 Crockford base32 characters where the first 10 encode a millisecond timestamp, so ULIDs sort chronologically while staying globally unique.

Are these UUIDs cryptographically random?

Yes. The generator uses crypto.randomUUID() where available and otherwise crypto.getRandomValues(), both backed by the platform's cryptographically secure random number generator.

Is anything sent to a server?

No. Every value is generated locally in your browser. Nothing about your IDs is uploaded, logged, or stored anywhere.

Can I generate a really large batch?

You can generate up to 100,000 IDs at once. Only the first 200 are shown in the preview for performance, but the full set is included in any copy or download.

Why are my ULIDs nearly identical at the start?

The first 10 characters of a ULID encode the current millisecond timestamp, so IDs created in the same millisecond share that prefix. The trailing 16 characters are random and keep each value unique.

Bulk UUID / ULID Generator

A UUID (Universally Unique Identifier) is a 128-bit value used as a database primary key, message ID, or correlation token when you need an identifier that is unique without a central coordinator. A ULID solves the same problem but encodes a timestamp at the front, so the IDs sort in creation order — handy for time-ordered records and index locality. This free tool generates either kind in bulk, entirely in your browser.

How it works

UUID v4 is built from 122 random bits with six bits fixed to mark the version (4) and variant (RFC 4122). This tool calls crypto.randomUUID() when the browser provides it, and otherwise fills 16 random bytes from crypto.getRandomValues() and sets the version and variant bits manually.

ULID is a 26-character string in Crockford base32. The first 10 characters encode the current time as a 48-bit count of milliseconds since the Unix epoch; the remaining 16 characters carry 80 bits of randomness. Because the timestamp leads, ULIDs created later always sort after earlier ones.

Tips and example

A UUID v4 looks like f47ac10b-58cc-4372-a567-0e02b2c3d479, while a ULID looks like 01ARZ3NDEKTSV4RRFFQ69G5FAV. Use ULIDs when you want sortable keys (for example, event logs) and UUIDs when ordering does not matter or you specifically want unpredictability. For seeding a database, download the CSV — it includes an index column alongside each value so you can map rows back to their source.