Academic and commercial experience with skeleton-based systems has demonstrated the benefits of the approach but also the lack of methods and tools for algorithm design and performance prediction. We propose a (graphical) transformation tool based on a novel internal representation of programs that enables the user to effectively deal with program transformation. Given a skeleton-based language and a set of semantic-preserving transformation rules, the tool locates applicable transformations and provides performance estimates, thereby helping the programmer in navigating through the program refinement space.