Could you provide JSONSchema for specification of App Definition? JSONSchema is well-adopted format to document in machine-readable way structure of documents like JSON. YAML too. The specification in this format can be used to create by community various tools to support the management of App Definition, i.e. liners, GitHub Actions with a liner, and auto-completion in IDE. I would recommend generating the current HTML documentation also based on the App Definition specification to keep it always up-to-date.
Examples of alternative specifications for YAML files:
A lot of IDE have support for JSONSchema for autocomplete of JSON / YAML files eg. Visual Studio Code ( https://code.visualstudio.com/docs/languages/json ).