Universally Unique Lexicographically Sortable Identifier

UUID can be suboptimal for many uses-cases because:

• It isn't the most character efficient way of encoding 128 bits of randomness
• The string format itself is apparently based on the original MAC & time version (UUIDv1 from Wikipedia)
• It provides no other information than randomness

• 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)

Implementations in other languages

From the community!

| Language | Author | | -------- | ------ | | Javascript | alizain | | Erlang | savonarola | | Elixir | merongivian | | Go | imdario | | Java | Lewiscowles1986 | | Julia | ararslan | | .NET | RobThree | .NET | fvilers | PHP | Lewiscowles1986 | | Python | mdipierro | | Ruby | rafaelsales |

Specification

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

01AN4Z07BY      79KA1307SR9X4MV3
|----------|    |----------------|  Timestamp          Randomness   10 chars           16 chars    50bits             80bits    base32             base32

Components

Timestamp

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

• 80 bits
• Cryptographically secure source of randomness, if possible

Sorting

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

Encoding

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

0123456789ABCDEFGHJKMNPQRSTVWXYZ

Binary Layout and Byte Order

The components are encoded as 16 octets. Each component is encoded with the Most Significant Byte first (network byte order).

0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      32bituinttimelow                     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     16bituinttimehigh     |       16bituint_random      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       32bituint_random                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       32bituint_random                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

String Representation

ttttttttttrrrrrrrrrrrrrrrr
where t is Timestamp r is Randomness

Prior Art

Partly inspired by:

• instagram-engineering
• firebase