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About

ULID Generator

A ULID is ready as the window opens: 26 characters, the first ten the time in milliseconds and the last sixteen random, so ULIDs sort by when they were made as plain text. Make up to a thousand, in capitals or lower case, and paste one into Inspect to read its time and the UUID it equals.

What it does

  • Crockford’s base32 leaves out I, L, O and U, so a ULID read aloud or copied by hand has no 1-or-l mix-ups.
  • ULIDs from one millisecond count up by one, as the spec’s monotonic generator does, so they stay in order.
  • Inspect reads a ULID in either case, and gives its time in UTC and its 128 bits as a UUID.
  • A ULID starting with 8 or above, or holding a letter outside the alphabet, is refused with the reason.
  • Copy them as lines, a JSON array or an SQL list, or download them.
  • The time runs out in the year 10889, when 48 bits of milliseconds are used up.

How to use it

  1. Set how many ULIDs, from one to a thousand.
  2. Tick Lower case if your system writes them that way.
  3. Copy the list in the form you need, or download it.
  4. Paste a ULID into Inspect to read the time it holds.

What it does not do

  • A count across servers: the counting up happens within one generator, so two servers’ ULIDs from one millisecond fall in random order.
  • Hiding the creation time: anyone can read it from the first ten characters.

Questions

ULID or UUID v7?

Both put 48 bits of milliseconds first and sort by time. A ULID is 26 characters with no hyphens, easy to read out; a UUID v7 fits a uuid column and every library that expects a UUID. Inspect turns a ULID into its UUID form when you need both.

Are ULIDs case-sensitive?

No. Capitals are the usual form, but a ULID in lower case means the same 128 bits, and Inspect reads either. Keep one case in storage, since a text column sorts capitals and lower case apart.

How many can be made in one millisecond?

More than anyone needs: the random part is 80 bits, and it counts up by one for each ULID in the same millisecond. A thousand made at once come out in order, those in one millisecond counting up from the first.

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