For a growing number of firms, it is important that life-cycle assessments (LCAs) as well as the interpretation of the results obtained be carried out directly by the design teams. Unfortunately, the complexity of these two elements hinders the development of really eco-designed products. In this paper, we propose a generic approach allowing a company to develop a specific environmental assessment tool which enables designers to carry out simplified environmental assessments during the design process. To be more precise, the generic approach is based on the creation of two main features: impact functions to simplify the inherent complexity of LCAs and an environmental categorisation per product range to facilitate the use of environmental assessment results by the design team. This paper presents the development of such tool (named EcoT) in the context of automotive part suppliers and demonstrates its technical robustness on two case studies (dashboards and door panels). At the end of the paper, we discuss the usability and appropriability of the EcoT tool based on handling tests carried out by the company design team.