Abstract—Continuously shrinking feature sizes cause an increasing vulnerability of digital circuits. Manufacturing failures and transient faults may tamper the functionality. Automated support is required to analyze the fault tolerance of circuits. In this paper, ROBUCHECK is presented - a design tool to analyze the fault tolerance of digital circuits. Engines based on simulation and formal methods are integrated to identify components that require additional fault protection. Consequently, an overall estimation of fault tolerance of the circuit is determined.