We present the architecture of the Rosser toolkit that allows optimisations to be specified in a domain specific language, then compiled and deployed towards optimising object programs. The optimisers generated by Rosser exploit model checking to apply dataflow analysis to programs to find optimising opportunities. The transformational language is derived from a formal basis and consequently can be proved sound. We validate the technique by comparing the application of optimisers generated by our system against hand-written optimisations using the Java based Scimark 2.0 benchmark.