Custom headers for HTTP statuses in Ruby on Rails

Adding headers for specific HTTP statuses in Ruby on Rails can be easily accomplished using super for render.

In your app/controllers/application_controller.rb:

def render(*args)
  super.tap do 
    if (400..599).cover?(response.status)
      response.headers['X-Custom-Error'] = '1'

There’s a lot you can do with this. As your application grows in complexity, using this pattern can help you communicate between your app and things like a reverse proxy.