Programming language: Go
License: MIT License
Tags: UUID    

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Globally Unique ID Generator

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

Xid uses the Mongo Object ID algorithm to generate globally unique ids with a different serialization (base64) to make it shorter when transported as a string: https://docs.mongodb.org/manual/reference/object-id/

  • 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 machine/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
  • Lock-free (i.e.: unlike UUIDv1 and v2)

Best used with zerolog's RequestIDHandler.


  • Xid is dependent on the system time, a monotonic counter and so is not cryptographically secure. If unpredictability of IDs is important, you should not use Xids. It is worth noting that most other UUID-like implementations are also not cryptographically secure. You should use libraries that rely on cryptographically secure sources (like /dev/urandom on unix, crypto/rand in golang), if you want a truly random ID generator.



go get github.com/rs/xid


guid := xid.New()

// Output: 9m4e2mr0ui3e8a215n4g

Get xid embedded info:



Benchmark against Go Maxim Bublis's UUID.

BenchmarkXID            20000000            91.1 ns/op        32 B/op          1 allocs/op
BenchmarkXID-2          20000000            55.9 ns/op        32 B/op          1 allocs/op
BenchmarkXID-4          50000000            32.3 ns/op        32 B/op          1 allocs/op
BenchmarkUUIDv1         10000000           204 ns/op          48 B/op          1 allocs/op
BenchmarkUUIDv1-2       10000000           160 ns/op          48 B/op          1 allocs/op
BenchmarkUUIDv1-4       10000000           195 ns/op          48 B/op          1 allocs/op
BenchmarkUUIDv4          1000000          1503 ns/op          64 B/op          2 allocs/op
BenchmarkUUIDv4-2        1000000          1427 ns/op          64 B/op          2 allocs/op
BenchmarkUUIDv4-4        1000000          1452 ns/op          64 B/op          2 allocs/op

Note: UUIDv1 requires a global lock, hence the performance degradation as we add more CPUs.


All source code is licensed under the MIT License.

*Note that all licence references and agreements mentioned in the xid README section above are relevant to that project's source code only.