Load custom validators in Rails 4

application.rb

module Macchiato
  class Application < Rails::Application
    config.autoload_paths += Dir[Rails.root.join('lib', 'validators').to_s]
  end
end

email_validator.rb

class EmailValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    unless value =~ /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i
      record.errors[attribute] << (options[:message] || "is not an email")
    end
  end
end