This paper describes the Korat tool for constraint-based generation of structurally complex test inputs for Java programs. Korat takes (1) an imperative predicate that speci fies the desired structural integrity constraints and (2) a finitization that bounds the desired test input size. Korat generates all inputs (within the bounds) for which the predicate returns true. To do so, Korat performs a systematic search of the predicate's input space. The inputs that Korat generates enable bounded-exhaustive testing for programs ranging from library classes to stand-alone applications.