Add to your Gemfile:

gem 'cuit_validator'

Run:

bundle install

Then add the following to your model:

validates :my_cuit, :cuit => true

If you need to validate the cuit outside a model:

CuitValidator.valid?('20-11111111-2') # boolean

This gem is thread safe, with one caveat: CuitValidator.default_options must be configured before use in a multi-threaded environment. If you configure default_options in a Rails initializer file, then you're good to go since initializers are run before worker threads are spawned.