This is a simple web IDE for designing and building Tree Languages. To build a Tree Language, you write code in a "grammar language" in the textarea on the left. You can then write code in your new language in the textarea on the right. You instantly get syntax highlighting, autocomplete, type/cell checking, suggested corrections, and more.
Click "New" to create a New Language, or explore existing languages. In dev tools, you can access the parsed trees below as "app.grammarProgram" and program at "app.program". We also have a work-in-progress checklist for creating new Tree Languages.