Database modeling is a key activity towards the fulfillment of storage requirements. Despite the availability of several database modeling tools for developers, these often come with associated costs, setup complexities, usability challenges, or dependency on specific operating systems. In this paper we present ONDA, a web-based tool developed at the University of Coimbra, that allows the creation of Entity-Relationship diagrams, visualization of physical models, and generation of SQL code for various database engines. ONDA is freely available at https://onda.dei.uc.pt and was created with the intention of supporting teaching activities at university-level database courses. At the time of writing, the tool being used by more than three hundred university students every academic year.