Describe the bug
In your Actions, you could respond to different formats based on the accepted format. Normally it might just be html, but you may have something that looks like:

get "/me" do
  if ajax?
    json({email: current_user.email})
  else
    html ShowPage
  end
end

To Reproduce

accepted_formats [:html, :ajax], default: :html

Comparisons to booleans are not pointless if the other operand is a union containing Bool:

def f(x : Int32 | Bool)
  print 1 if x == true
  print 2 if x == false
  print 3 if x
  print 4 if !x
  puts
end

f(0)     # 3
f(true)  # 13
f(false) # 24

(Comparisons to unions not containing Bool are still pointless, as they should always evaluate to false.)