Architecture decisions are often not explicitly documented in practice, even though explicit capturing and documentation of architecture decisions has been associated with a multitude of benefits. Several decision documentation tools have been proposed but they often do not meet the expectations and needs of the industry. As part of a research collaboration with ABB, we developed a decision documentation tool that aims to ensure industrial applicability. This tool is an add-in for Enterprise Architect and is an implementation of a viewpoint-based decision documentation framework. To validate the add-in, we conducted a case study with architects from ABB. In this study, we assessed to what extent and why software architects intend to use our approach. We therefore investigated the perceived usefulness, perceived ease-of-use, and contextual factors threat influence the architect’s intention to use the tool. We found that the tool has a high relevance for software architects, that it increases the quality of decision documentation and that it improves productivity of architects in various ways. With respect to ease-of-use, the study identified the need for better guidelines. With respect to contextual factors, we found several factors that influence the intention to use the add-in in an industrial environment.