An entity modeling system integrated with a low-code application development platform may have a web/mobile-based user interface that can run in a browser environment on user devices ranging from desktop computers to smart phones. Users such as a subject matter expert may access an entity model designer tool of the system to model an entity. Responsive to user interaction with an entity composition function, the system may access a data store over a network and generate a view including a collection of entity building block(s) retrieved from the data store. Responsive to the user selecting a first entity building block from the collection to add to the entity, the system may automatically extend the entity to include settings of the first entity building block. The settings may include at least one of a property, permission, action, behavior, or resource to the entity.