Universally Unique Lexicographically Sortable Identifier for Lua

Based on the implementation by alizain

UUID can be suboptimal for many uses-cases because:

  • It isn’t the most character efficient way of encoding 128 bits of randomness
  • UUID v1/v2 is impractical in many environments, as it requires access to a unique, stable MAC address
  • UUID v3/v5 requires a unique seed and produces randomly distributed IDs, which can cause fragmentation in many data structures
  • UUID v4 provides no other information than randomness which can cause fragmentation in many data structures

Instead, herein is proposed ULID:

  • 128-bit compatibility with UUID
  • 1.21e+24 unique ULIDs per millisecond
  • Lexicographically sortable!
  • Canonically encoded as a 26 character string, as opposed to the 36 character UUID
  • Uses Crockford’s base32 for better efficiency and readability (5 bits per character)
  • Case insensitive
  • No special characters (URL safe)



 luarocks install ulid


local ulid_mod = require("ulid")

print(ulid_mod.ulid())  -- 01ARZ3NDEKTSV4RRFFQ69G5FAV


Below is the current specification of ULID as implemented in this repository.

Note: the binary format has not been implemented.

  01AN4Z07BY      79KA1307SR9X4MV3

 |----------|    |----------------|
  Timestamp          Randomness
    48bits             80bits



  • 48 bit integer
  • UNIX-time in milliseconds
  • Won’t run out of space till the year 10895 AD.


  • 80 bits
  • Please make sure to use cryptographically secure source of randomness, if possible


The left-most character must be sorted first, and the right-most character sorted last (lexical order). The default ASCII character set must be used. Within the same millisecond, sort order is not guaranteed


Crockford’s Base32 is used as shown. This alphabet excludes the letters I, L, O, and U to avoid confusion and abuse.


String Representation


 t is Timestamp
 r is Randomness

Test Suite

Tests can be run from the repo using busted

generated by LDoc 1.4.6 Last updated 2017-03-28 14:40:33