The rapid influx of low-quality data visualisations is one of the main challenges in today's communication. Misleading, unreadable, or confusing visualisations spread misinformation, failing to fulfill their purpose. The lack of proper tooling further heightens the problem of the quality assessment process. Therefore, we propose VisQualdex, a systematic set of guidelines isnpired by the Grammar of Graphics for evaluating the quality of data visualisations. To increase the practical impact of VisQualdex, we make these guidelines available in the form of the web server, visqual.info.