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xid is a globally unique id generator thought for the web

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Globally Unique ID Generator

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Package xid is a globally unique id generator library, ready to be used safely directly in your server code.

Xid is using Mongo Object ID algorithm to generate globally unique ids with a different serialization (bast64) to make it shorter when transported as a string:

  • 4-byte value representing the seconds since the Unix epoch,
  • 3-byte machine identifier,
  • 2-byte process id, and
  • 3-byte counter, starting with a random value.

The binary representation of the id is compatible with Mongo 12 bytes Object IDs.
The string representation is using base32 hex (w/o padding) for better space efficiency
when stored in that form (20 bytes). The hex variant of base32 is used to retain the
sortable property of the id.

Xid doesn't use base64 because case sensitivity and the 2 non alphanum chars may be an
issue when transported as a string between various systems. Base36 wasn't retained either
because 1/ it's not standard 2/ the resulting size is not predictable (not bit aligned)
and 3/ it would not remain sortable. To validate a base32 xid, expect a 20 chars long,
all lowercase sequence of a to v letters and 0 to 9 numbers ([0-9a-v]{20}).

UUIDs are 16 bytes (128 bits) and 36 chars as string representation. Twitter Snowflake
ids are 8 bytes (64 bits) but require machine/data-center configuration and/or central
generator servers. xid stands in between with 12 bytes (96 bits) and a more compact
URL-safe string representation (20 chars). No configuration or central generator server
is required so it can be used directly in server's code.

Name Binary Size String Size Features
UUID 16 bytes 36 chars configuration free, not sortable
shortuuid 16 bytes 22 chars configuration free, not sortable
Snowflake 8 bytes up to 20 chars needs machin/DC configuration, needs central server, sortable
MongoID 12 bytes 24 chars configuration free, sortable
xid 12 bytes 20 chars configuration free, sortable


  • Size: 12 bytes (96 bits), smaller than UUID, larger than snowflake
  • Base32 hex encoded by default (20 chars when transported as printable string, still sortable)
  • Non configured, you don't need set a unique machine and/or data center id
  • K-ordered
  • Embedded time with 1 second precision
  • Unicity guaranteed for 16,777,216 (24 bits) unique ids per second and per host/process

Best used with xlog's



go get github.com/rs/xid


guid := xid.New()

// Output: 9m4e2mr0ui3e8a215n4g

Get xid embedded info:



All source code is licensed under the MIT License.

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