ULID vs UUID — which should I pick?

ULID when the id appears in URLs or must sort by time and 26 characters is a win. UUID v7 when your stack already has a native UUID type and you want the same properties inside it.

Are ULIDs case sensitive?

The spec writes them in uppercase Crockford base32 and readers are expected to treat I/L/O/U as the nearest digit, so comparison should be case-insensitive. Lowercase output is fine to store.

How many ids can I make before a collision?

80 random bits per id within a single millisecond. That is comfortably safe at ordinary application rates; at more than a few billion ids per millisecond you are past what a ULID is for.

Generators & Utilities Ready to use

ULID Generator

Generate ULIDs — 26-character Crockford base32 identifiers that sort lexicographically — with a live creation timestamp, in your browser.

Operation

Inspect reads the version, variant, node and (for v1/v7) the creation time baked into an id you paste.

ID format

v4 for opaque primary keys; v7 or ULID when rows should insert in creation order.

How many

Written as

Ignored for ULID, which never carries hyphens.

UPPERCASE

Seed (optional)

Set a seed to get the same batch again — useful for fixtures and tests.

ID to inspect

This tool runs entirely in your browser. Your input never leaves your device.

About ULID Generator

A ULID is 128 bits written as 26 uppercase-friendly characters instead of 36. The first 10 encode a 48-bit millisecond timestamp; the last 16 carry 80 random bits. Like UUID v7 it sorts by creation time, but it is shorter, alphabet-safe for URLs, and needs no hyphens — which is why it is popular for public identifiers in APIs, invoice numbers, and anything a human might type.

It is not a UUID. Its format is its own spec, the alphabet excludes I, L, O and U to avoid transcription errors, and some validators will reject one pasted into a UUID field. Generate both if you are still choosing.

One honest caveat this page will not hide: ULIDs minted inside the same millisecond share their first 10 characters and are ordered only by their random tail, so strict monotonicity needs the generator to bump the random part on a repeat — the standard 'monotonic within a millisecond' rule. Batches here are drawn per click, so ids created in one run may tie on the timestamp prefix. Sort by the id and you get creation order at millisecond resolution, nothing finer.