This paper presents a flexible tool which supports the decision making process involved in defining post-editing guidelines. It is inspired by the work of O’Brien (2012) towards a translation quality assessment model, briefly reviewed here with a view to adapting it to post-editing specifications. The paper first presents a review of the relevant literature on post-editing, followed by an account of the challenges involved in defining post-editing rules. The different components of the decision tool are then presented and illustrated with examples. Finally, a discussion of its effectiveness is advanced together with some indications for further work.