A ULID (Universally Unique Lexicographically Sortable Identifier) is a 128-bit unique identifier. The first 48 bits are a millisecond timestamp and the remaining 80 bits are random, encoded as a 26-character Crockford Base32 string. Because it starts with a timestamp, ULIDs sort in creation order as plain strings, which makes them a popular alternative to UUIDs.

ULID Generator - Lexicographically Sortable Unique IDs (Free, 26-char Base32)

Q: How is ULID different from UUID?

UUID v4 is fully random and has no meaningful sort order. ULID embeds a timestamp at the front, so sorting the strings lexicographically also sorts them by creation time, which helps database indexes and time-ordered listings. ULIDs are 26 characters with no hyphens, shorter than a 36-character UUID and friendlier in URLs.

Q: Are the generated ULIDs safe?

Yes. ULIDs are generated entirely in your browser (JavaScript) using the cryptographically secure crypto.getRandomValues. Nothing is sent to a server.

ULID structure and when to use it

Structure (timestamp plus randomness)

A ULID is 128 bits: the first 48 bits are milliseconds since 1970 and the remaining 80 bits are random. It is encoded in Crockford Base32 (A-Z and digits, excluding ambiguous letters) into a 26-character string. Because the timestamp comes first, ULIDs generated in different milliseconds sort in creation order.

ULID vs UUID

Use UUID v4 when you only want randomness, and ULID when you want a time-ordered primary key. ULIDs tend to insert near the end of a B-tree index, reducing fragmentation. If you must not leak creation time, prefer a random UUID v4 instead.

Lowercase output and count

The canonical ULID form is uppercase, but you can output lowercase for systems that expect it (the value is the same). You can generate up to 1000 at once. Randomness uses crypto.getRandomValues.

Frequently asked questions (FAQ)

What is a ULID?

A 128-bit unique identifier whose first 48 bits are a millisecond timestamp and remaining 80 bits are random. It is encoded as a 26-character Crockford Base32 string and sorts in creation order as plain text. It is used as a UUID alternative.

How is ULID different from UUID?

UUID v4 is fully random with no sort order, while ULID's leading timestamp makes lexical order equal creation order. ULIDs are 26 characters (vs 36 for UUID) with no hyphens, so they are also URL-friendly.

Are the generated ULIDs safe?

Yes. They are generated entirely in your browser using the cryptographically secure crypto.getRandomValues. Nothing is sent to a server.