MSaaS (M&S as a Service) is gaining momentum as an effective approach to bring the benefits of service-oriented architectures and cloud computing into the M&S field, so as to enhance interoperability, composability, reusability and reduce the cost of M&S efforts. Such significant advantages can be further enhanced by introducing automated model transformations that support the various phases of a M&S effort, from simulation model building down to model implementation, deployment and execution. In previous contributions we have already addressed the use of automated model transformations that can be effectively adopted to provide simulation services for MSaaS platforms. This paper instead focuses on the automated development of modeling services for MSaaS, i.e., those services that allow platform users to easily build models in their own modeling language by use of a web-based user interface. Specifically, this work proposes an approach to automatically generate web-based visual editors from a metamodel that defines a given modeling language. Once generated, such editors can be made available on demand through a complete MSaaS platform, which also includes simulation services. The paper first describes the architecture of a MSaaS platform that includes modeling services, then illustrates the method for the automated development of web-based modeling services and, finally, gives a complete example application of the proposed method. ©2017 Society for Modeling & Simulation International (SCS).