Over recent decades, comparative political scientists have developed new measures at a rate of knots that evaluate the quality of democratic regimes. These indices have been broadly applied to assess the quality of democracy cross-nationally and to test the generalisability of theories regarding its causes and effects. However, the validity of these inferences is jeopardised by the fact that the quality of democracy is an abstract and contested concept. In order to address this eventuality, researchers constructing indices measuring the quality of democracy as well as researchers applying these indices should critically examine the quality of the indices. Owing to the absence of a standardised framework that is both suitable for the evaluation of contested concepts and that includes explicit coding rules so as to be directly applicable, this article seeks to fill this gap. The application of our framework is demonstrated by an evaluation of the Sustainable Governance Indicators, the Global Democracy Ranking and the Democracy Barometer. As indicated by our evaluation, the framework is a practical tool that helps to assess the conceptual foundation, validity, reliability and replicability of indices. In addition, it can be used to study the quality of indices in a comparable manner.