ULID Generator

ULIDs work as primary keys, event IDs and object names when you want identifiers that need no central counter and that sort by creation time as plain text. A UUID v7 sorts the same way; a ULID is the shorter form, 26 characters against 36, with no hyphens and only letters and digits, so it drops into a URL or a file name unchanged. Generate 1 to 500 at once, switch to lower case, separate them with newlines, commas, spaces or tabs, and copy the batch. The decoder takes an existing ULID and shows when it was created.

A ULID made at 2026-10-13 09:30:00.000 UTC begins with 01M4T9HVE0, which is the millisecond timestamp 1,791,883,800,000 in base 32.

ULID = timestamp (10 characters, 48 bits) + randomness (16 characters, 80 bits), 26 characters of Crockford base32: 0123456789ABCDEFGHJKMNPQRSTVWXYZ, with no I, L, O or U.

The timestamp is Date.now() written in base 32, most significant digit first. Each random character comes from one byte of crypto.getRandomValues taken modulo 32. Because 256 is a multiple of 32, every character is uniform, and 16 characters × 5 bits give the 80 random bits.

IDs from different milliseconds sort by time. The generator uses the spec's monotonic mode: when an ID is made in the same millisecond as the one before it, as most of a batch are, its random part is the previous one plus 1 (carrying across the 16 characters) instead of a fresh draw, so a batch sorts in creation order as plain text. A clock that steps back keeps the last timestamp. Only the first ID of each millisecond gets fresh random bits, so the rest of that millisecond's IDs are predictable from it.

The decoder upper-cases its input, requires exactly 26 base32 characters and turns the first ten into a date. It rejects a first character above 7, because the 48-bit timestamp tops out at 7ZZZZZZZZZ, and shows a message saying so. It does not read I, L or O as 1 and 0.