In complex self-checking systems several blocks (i.e. functional blocks and checkers) are embedded. In order to check the self-checking properties of such blocks we need to know the set of vectors they receive from the blocks feeding their inputs (i.e. the code word output spaces of the source blocks). In a complex system the computation of the output spaces by means of exhaustive simulation of the system is intractable. In this paper we present a tool which performs this computation with low CPU time. Some other tools allowing to verify the self-checking properties of embedded blocks (like the strongly fault secure property of embedded PLAs and the self-testing property of embedded checkers), have also been developed and experimented.