The Department for the Regulation and Control of Magical Creatures gives classifications to all know beasts, beings and spirits. Theses offer an at-a-glance guide to the perceived dangerouness of a creature. The five categories are as follow:
Ministry of Magic (M.O.M.) Classification
XXXXX - Known wizard killer / impossible to train or domesticate
XXXX - Dangerous / requires specialist knowledge / skilled wizard may handle
XXX - Competent wizard should cope
XX - Harmless / may be domesticated
X - Boring
References[]
Fantastic Beasts and Where to Find Them, Newt Scamander