This tool demo paper describes a tool called XToF which is being developed through a collaboration between the University of Victoria, the University of Namur and the University of Waterloo. The purpose of the tool is to let programmers define, maintain, visualise and exploit precise traceability links between a feature diagram and the code base of a software product line. The resulting tool supports automated configuration of a Java or C code base and is minimally intrusive with respect to development practices.