Version 3.0 is not released. gem install nanoid still installs 2.0.1. Read that version's documentation in the v2.x README.

On Ruby 3.3+ the same 21-character ID can be made without this gem:

alphabet = "_-0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
SecureRandom.alphanumeric(21, chars: alphabet.chars)

The published 2.0.1 implementation is faster. Both calls below use size 21 and the default NanoID alphabet (benchmark-ips, 2s warmup, 5s run, Ruby 3.3.12, arm64):

SecureRandom.alphanumeric is 1.78× slower.

The rest of this page describes unreleased 3.0 work on master. It requires Ruby >= 3.3. For NanoID 1.x compatibility, see branch v1.x.

A tiny, secure URL-friendly unique string ID generator.

Ruby implementation of original NanoID https://github.com/ai/nanoid

Starting with 3.0, Nanoid.generate is a thin wrapper around Ruby's own SecureRandom.alphanumeric/Random.alphanumeric (stdlib, Ruby >= 3.3), rather than a hand-rolled random ID algorithm. It still fixes a couple of edge cases those stdlib methods get wrong: a single-character or empty alphabet makes Random::Formatter#choose loop forever, and a negative size is silently returned as '' instead of raising.

Into Gemfile / gems.rb add:

gem 'nanoid'

require 'nanoid'

Nanoid.generate

Size: 21 character length

Alphabet: _-0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ

Non secure: false

require 'nanoid'

Nanoid.generate
# => "MVNBLMwrcdbKjpo73qsmN"

require 'nanoid'

Nanoid.generate(size: 10)
# => "zRTPzok801"

require 'nanoid'

Nanoid.generate(alphabet: '1234567890abcdef')
# => "84e292c6aabbbf50bf087"

require 'nanoid'

Nanoid.generate(size: 14, alphabet: '1234567890abcdef')
# => "c5db3470fadf94"

require 'nanoid'

Nanoid.generate(non_secure: true)
# => "-BX3dH02BmRX9Al4drpIb"