The department of regulations and control of magical creatures give classifications to all known , beasts, spirits and beings .These offer an at a glance guide to the perceived dangerousness of a creature .The five catogeries are as follow :

Ministry of Magic classifications

xxxxx: Known wizard killer / impossible to train or domesticate or anything Hagrid likes

xxxx: Dangerous /requires specialist knowledge /skilled wizard may handle

Xxx Competent wizards should cope

xx Harmless/may be domesticated
x boring