It is a stag beetle. They also come in other colors, and some can grow over 3 inches. They are well-known for their big mandibles, which they use to fight.
How large is it? There are thousands of black bugs with pincers of all sizes and shapes, some are harmless and some are not. There are some great books in the library and some great entomology resources online to help you identify what it is.
Many black bugs with pincers are from the beetle family. For instance the giant stag beetle is black and has pincers. The scarites subterraneus is also a black beetle with pincers. Another very common bug that is black with pincers is the earwig. They are a dark blackish brown bug with pincers.
Without knowing more, it will be impossible to completely identify the insect in question. However, I would assume it would be some type of beetle. See if it has 6 legs and its back is split into 2 wings or wing covers.
A small flat black or dark brown bug with its head at one end what looks like pincers at hte other end is call an earwig. (Deraptera} The pincer like thigs are called cerci.
