LeanCheck is a simple enumerative property-based testing library. Properties are defined as Haskell functions returning a boolean value which should be true for all possible choices of argument values. LeanCheck applies enumerated argument values to these properties in search for a counterexample. Properties can be viewed as parameterized unit tests. LeanCheck works by producing tiers of test values: a possibly infinite list of finite sublists of same-and-increasingly-sized values.