Web services are meant to be used by other programs. Developers (or other programs) need to understand how to interact with them, which means documentation is crucial. Some standards like OpenAPI define ways to document web services and target both humans and programs. Many tools can be used to help developers to work in a forward engineering process: they use hand-written OpenAPI models as input and automatically generate a skeleton of a working application, for example. However, this approach is not suitable to generate working applications if several evolutions occur over time, which often results in a misalignment between the OpenAPI model and the web services implementation. Here we show how we extend the OpenAPI 3.0 specification to allow building actual web services using a Model-Driven Engineering (MDE) approach. We extend the SWSG tool to make it possible to generate code from an extended OpenAPI model. This leverages a MDE approach to build web services from a model while benefiting from OpenAPI 3.0 tooling and ecosystem.