Helpers

Helpers are just modules with helping private methods for Controllers:

# controllers/api_controller.rb

module MyProject
  class APIController < Flame::Controller
    include APIHelper

    def index
      { result: 'success', data: 'Welcome!' }
    end
  end
end

# helpers/api_helper.rb

module MyProject
  module APIHelper
    # Method for after-hook in controller above
    def to_json(content = body)
      response.headers[Rack::CONTENT_TYPE] = 'application/json; charset=utf-8'
      body JSON.generate(content)
    end

    protected

    # Method for overriding controller executing (any route)
    # Must be protected
    def execute(method)
      # before hooks
      check_access!
      # You can also check which method is calling (`method` argument)
      super # execute calling method
      # after hooks
      to_json body
    end
  end
end

But often such things can be just private methods of the correct base controller.