Abstract: The present invention provides a system, method and computer program for determining constraint errors in hardware design debugging. The invention may be included as part of a complete verification solution. The method involves applying a diagnostic technique such that under-constrained problems are identified by adding a model-free error suspect or error candidate on the primary input signals (or other signals where constraints or stimuli are usually added). The present invention also provides a system, method and computer program that enables hardware design correction, consisting of the use of generating correction waveforms for identifying one or more corrections at the gate level and/or logic level of the hardware design. A number of different diagnostic techniques can be used in this way for example, include simulation-based techniques, BDD-based techniques, SAT-based techniques and path tracing.