The need for adequate instruments to support practitioners toward achieving sustainable and energy-efficient architectural and urban design has long been acknowledged. Motivated by identified shortcomings of building performance assessment tools for conceptual neighborhood-scale design, this paper proposes a novel workflow to enable practitioners to efficiently explore a space of design alternatives and compare them in terms of their energy and daylight performance. The workflow includes a multi-criteria optimization algorithm, which is coupled to a performance assessment engine based on predictive mathematical models. To get some insight on the potential added value for design and the usability of this approach in practice, the workflow has been implemented as a plug-in to an existing 3D modeling software and subsequently tested by practitioners during workshops, notably on real projects provided by the participants. Outcomes from the workshops, which include responses from the participants to a pre- and post-test survey, are presented. Results highlight the relevance of the proposed workflow for informing decisions about early-stage building massing on the basis of the considered performance criteria. Improvements envisioned for both the workflow and its implementation are highlighted and discussed.