A mechanism for providing equation-level diagnostic error messages for system models undergoing circuit simulations is discussed. The components in a model of a system being simulated are converted into multiple numerical equations where each equation corresponds to a component in the system being simulated or a topology equation for the system model. Each numerical equation is numerically analyzed in order to identify illegal configurations in the system. Upon detection of an error, an error message listing the components associated with the illegal configuration is generated for the user.