This paper examines the process of designing assessment and how teachers in higher education, who are developing blended learning materials, can be supported to consider their approach to assessment and to select from the range of assessment opportunities that are becoming available. The paper presents the design and evaluation of an online decision support tool for assessment design, which was developed on a collaborative project across Indian and European universities. The tool was designed based on a shared framework of design and assessment principles which took account of the purpose of the assessment, knowledge and skills to be assessed and how and by whom the assessment was to be conducted. The tool was not intended to provide definitive advice but rather to support the decision-making process and professional development of teachers. This support would be provided during the use of the tool and as a summary at the end of the teacher’s consultation with the tool. Overall, users were satisfied with the tool, as the data show, and were positive about using it in designing assessment. Recommendations that were made during the evaluation, for redeveloping the tool to make it more suitable for a wider audience are discussed.