In this thesis, an IT company asked for a tool for improving some aspects of daily work for employees working with customer support. A web-site was constructed for this purpose, and development was steered by applying usability evaluation methods in an iterative manner. These methods were combined with the approach of following the guidelines of user-centered design. The aim was to see if an increase of user-satisfaction towards the user-interface could be measured between iterations.Another significant question that was central to the study was the comparison between the industry-leading Nielsen’s heuristics and Gerhardt-Powals principles. Only one previous study was found making this comparison which made it interesting to see if the same result would be reached in this study.