This paper presents a new approach for monitoring and estimating device reliability of nanometer-scale devices prior to fabrication. A four-layer architecture exhibiting a large immunity to permanent as well as random failures is used. A complete tool for a-priori functional fault tolerance analysis was developed. It is a statistical Monte Carlo based tool that induces different failure models, and does subsequent evaluation of system reliability under realistic constraints. A structured fault modeling architecture is also proposed, which is together with the tool a part of the new design method where reliability is considered as a central focus from an early development stage.