CODERU (COmmon DEpendency RUles) is a Java code quality tool to enforce good design in respect to package dependencies. Its rules rely on reserved package names, and the allowed dependency rules between them are expressed in a general way. Unlike other tools that force you to define allowed or disallowed individual package dependencies, CODERU is based on a fixed set of general rules. The dependencies between packages need not be defined explicitly. These general dependency rules are based on common design practices which are reflected in preserved package names: "api", "common", "impl", and "factory". It includes a tool for checking your code for rule conformance.