Using the werkzeug debugger if you're testing AJAX calls to your API.

gistfile1.txt

$(window).ajaxError(function(evt, evtData) {
  if(evtData && ('responseText' in evtData)) {
	  var debuggerWindow = window.open('about:blank', 'debuggerWindow');
	  debuggerWindow.document.open();
	  debuggerWindow.document.write(evtData.responseText);
	  debuggerWindow.document.close();
  }
});