ArgumentError (too few arguments): when calling format.json on rails 4.04

Mostly you would get the error ArgumentError (too few arguments): on the format when you forget to call this part of code within the block to respond_to method call.

Your code should actually look like

def action_name
  respond_to do |format|  ## Add this
    format.json { render json: {}, status: :ok}
    format.html 
    ## Other format
  end                    ## Add this
end