A ULID is a 26-character identifier made of a 48-bit timestamp followed by 80 bits of randomness, encoded in Crockford base32. It is lexicographically sortable by time, case-insensitive, and URL-safe — a popular alternative to UUIDs.

How is a ULID different from a UUID v7?

Both put a millisecond timestamp first so they sort by creation time. ULIDs use a compact 26-character base32 string, while UUID v7 keeps the canonical hyphenated hex format. ULIDs are shorter and avoid hyphens.

Why are ULIDs sortable by time?

The first 48 bits are a millisecond timestamp encoded as the leading 10 characters. Because Crockford base32 preserves order, sorting ULID strings alphabetically also sorts them by creation time, which is handy for database keys.

How many ULIDs can I generate before a collision?

Within a single millisecond there are 80 bits of randomness, giving 2^80 possible values, so collisions are astronomically unlikely. Across different milliseconds the timestamps already differ, so they can never collide.

Why does the tool offset each ULID by one millisecond in a batch?

When generating many at once it increments the timestamp per ULID so the batch stays strictly time-ordered and monotonic, rather than all sharing one timestamp and relying only on randomness for ordering.

Is Crockford base32 case-sensitive?

No. Crockford base32 excludes the ambiguous letters I, L, O and U and treats letters case-insensitively, so an uppercase and lowercase ULID represent the same value. The lowercase option is purely cosmetic.

Can I use a ULID as a primary key?

Yes — that is a common use. The time-sortable prefix keeps index inserts mostly sequential (reducing fragmentation versus random UUIDs) while the random suffix keeps each key unique and hard to guess.

ULID Generator — Gera Tools

Q: Are ULIDs generated privately?

Yes. The timestamp and 80 random bits come from your browser's Web Crypto, and nothing is uploaded — generation happens entirely on your device.

URL-safe ULID generator

A ULID (Universally Unique Lexicographically Sortable Identifier) is a 26-character identifier designed as a friendlier alternative to the UUID. It combines a 48-bit millisecond timestamp with 80 bits of randomness and encodes the result in Crockford base32, producing IDs that sort by creation time, contain no hyphens, and are safe to drop straight into URLs, filenames and log lines. This generator creates one ULID or a sortable batch of up to a thousand, all in your browser.

How it works

The 128 bits of a ULID are split into two parts and base32-encoded:

Timestamp (first 10 characters) — the current time in milliseconds since the Unix epoch, encoded as a 48-bit integer.
Randomness (last 16 characters) — 80 random bits drawn from the browser’s crypto.getRandomValues.

Crockford base32 uses the alphabet 0-9 and A-Z minus the ambiguous letters I, L, O and U. Because this encoding preserves byte order, sorting ULIDs as plain strings sorts them chronologically. When you request a batch, each ULID’s timestamp is incremented by one millisecond so the whole batch stays strictly ordered.

Example

A ULID generated now looks like 01ARZ3NDEKTSV4RRFFQ69G5FAV. The first ten characters 01ARZ3NDEK are the encoded timestamp; the remaining sixteen TSV4RRFFQ69G5FAV are random. Generate a batch of three and you get three IDs whose leading characters increase in lockstep, so they sort in creation order even before the random tail is considered.

Property	Value
Total length	26 characters
Timestamp bits	48 (first 10 chars)
Random bits	80 (last 16 chars)
Encoding	Crockford base32
Case-sensitive	No

Generation happens entirely on your device — the timestamp and random bits come from your browser’s Web Crypto, and nothing is uploaded.