This paper addressesthe shortcomings of the Spanishlegislative process, particularly in criminal matters, in order to make an appropriate laws effects' assessment to ensure their quality, their rationality. The author analyzes with that aim the different tasks currently performed along the phases in the law-making process in Spain and the instruments which public powers have to develop them. So, it reveals the purely formal nature of the work they perform in such phases, including laws assessment, claiming for the empowerment of material aspects of these tasks, especially because of the deficiencies identified at this point in the gestation latest criminal law reforms of 2010 and 2015.