Short description of WinProof 5.1: WinProof is a major advance over other grammar checkers. It goes beyond simple grammar checking and it can actually proofread like a person and catch non-English constructions created by careless typing errors like typing "it" when you meant "is". WinProof uses a revolutionary language processing system which knows what words can be combined and flags an error when it sees an illegal combination. It also has a built-in spell checker.