The tools API info.magnolia.ui.framework.tools is handy, since it allows to configure a sub-app with only a few lines of YAML.
However, with current classes one cannot configure a form tool to create or edit a JCR node; instead it requires (for instance) to extend FormToolPresenter and override #getItem.

Provide a subclass of FormTool with a definition class to configure the jcr node to bind to the form without any further need for custom java code.