The Devel module continues to be a primary method of assisting developers to debug their code. One of the things that's new in the version for Drupal 8 is Kint replacing Krumo as the library used to output debugging information. Using Kint offers a number of improvements over Krumo. The most significant is the ability to see private attributes of objects. Kint uses the PHP Reflection API to get all information about an object, where Krumo used get_object_vars().