Concerning net zero energy buildings, providing early design support for architects has never been more important. In this context, building performance simulation tools could be a strong supportive technique, when integrated early in the architectural design process. However, despite the available range of tools, most of them do not meet the architects' requirements. To identify this gap, this study compared the ‘architect-friendliness’ of six state-of-the-art simulation tools, to highlight the architects' requirements for these tools and to develop guidelines for researchers and tool developers. The examined tools included ECOTECT, IES/VE – Sketch-Up, Energy10, eQuest, HEED, and Design Builder. The analysis was based on an extensive list of criteria defining the user-friendliness of tools from an architect's point of view. The results show that no single tool is entirely adequate to assist the architect's decision-making process. One of the major limitations is the poor communication and visualization of the output results. ; Peer reviewed