Error analysis is very important in determining the error control capabilities of any code. Traditionally these are measured by analyzing BER performance. We have designed and implemented a visual debugging tool (VDT) for tracing trellis decoding process of a class of augmented array codes. We have implemented a user-friendly interface in utilizing the VDT for introducing errors at the specifically selected positions of the array. Also certain error patterns can be added to all possible array positions in sequence. The observation of the effect of these purposely inserted errors is facilitated by VDT interface. The VDT can be effectively employed to measure error detection and/or correction power of the Viterbi decoder. The tool allows users to trace decoding process step-by-step, so it can be utilized for teaching and research activities of code design and their practical applications.