ULID Generator (ULID / Crockford Base32 / Monotonic supported)

About This Tool

This tool generates ULIDs (Universally Unique Lexicographically Sortable Identifier). A ULID consists of a 48-bit epoch timestamp (milliseconds) and 80 bits of randomness, encoded into 26 characters with Crockford Base32 (0123456789ABCDEFGHJKMNPQRSTVWXYZ). You can choose the time source (Local / IANA / fixed offset) and the time to use (current or specified), and the UTC/local values shown in the preview always match the timestamp used for generation. By specification, the ULID timestamp is UTC milliseconds; the time zone only affects how it is displayed.

Time check

Generation & output

How to use

  1. In Time check, choose Local / IANA / Fixed offset (the defaults are usually fine).
  2. In Time to use, pick Current time or Specified datetime. When specifying, enter YYYY-MM-DDTHH:MM[:SS[.mmm]]; the preview and generation use that value.
  3. Set Quantity, toggle Monotonic generation if needed, then press Generate. Results appear line by line.

Additional notes

  • The preview shows the current UTC time and the local time for the selected source. The timestamp from the preview is used as-is when you generate.
  • IANA time zones determine offsets with daylight-saving time (DST) taken into account via iterative adjustment.
  • Each click re-initializes the randomness so you get a fresh sequence even with the same millisecond and settings.

Cautions

  • The ULID timestamp is always UTC epoch milliseconds; time zones affect only the display. When generating with the current time, switching time zones does not change the timestamp bits.
  • Only when Specified datetime is chosen is the entered wall-clock time converted to UTC (using the selected source) and applied to the timestamp.
  • Monotonic ON: the randomness increments within the same millisecond (monotonic ULID). OFF: randomness is fully shuffled.

What is a ULID?

A ULID is composed of a 48-bit millisecond timestamp and 80 bits of randomness, producing IDs that sort chronologically in ASCII order.
Like UUID v7, it is easy to order by time, and Crockford Base32 makes it safe for URLs and filenames (26 uppercase characters, excluding I/L/O/U for readability).