config/routes.rb

@@ -62,6 +62,8 @@ end
 
 get '/sitemap.xml' => 'sitemaps#index', defaults: { format: 'xml' }
 
+get "/robots.:format", to: "pages#robots"
+
 constraints(host: /^(?!www\.)/i) do
   match '(*any)' => redirect { |params, request|
     URI.parse(request.url).tap { |uri| uri.host = "www.#{uri.host}" }.to_s