Techniques disclosed herein relate generally to debugging complex computing systems, such as those executing neural networks. A neural network processor includes a processing engine configured to execute instructions to implement multiple layers of a neural network. The neural network processor includes a debugging circuit configured to generate error detection codes for input data to the processing engine or error detection codes for output data generated by the processing engine. The neural network processor also includes an interface to a memory device, where the interface is configured to save the error detection codes generated by the debugging circuit into the memory device. The error detection codes generated by the debugging circuit are compared with expected error detection codes generated using a function model of the neural network to identify defects of the neural network.