middleman--middleman/middleman-core/fixtures/extension-hooks-app/config.rb

set :layout, false

class MyFeature < Middleman::Extension
  def initialize(app, options_hash = {}, &block)
    super

    app.before do
      puts '/// before ///'
    end

    app.ready do
      puts '/// ready ///'
    end

    app.before_build do |_builder|
      puts '/// before_build ///'
    end

    app.after_build do |_builder|
      puts '/// after_build ///'
    end
  end

  def after_configuration
    puts '/// after_configuration ///'
  end
end

::Middleman::Extensions.register(:my_feature, MyFeature)

activate :my_feature