I believe what the commenter is suggesting is that since this is supposed to be machine readable then why not start with a common format like JSON similar to how things like MCP serve what functions are available or an OpenAPI spec. Generate the JSON and serve that from the well known directory.

People serve plain JSON all the time. This proposed standard is essentially a structured file anyway.. why not YAML? Why not INI? Getting away from bespoke unicorn file formats has been good for everyone.

JSON is great for code. It is heavy and deeply nested for Agents. The constraint is the context window. Brackets, quotes, and nesting are token tax. YAML is brittle. Whitespace errors break parsers. We chose the robots.txt model. It is dense and resilient. It is not a unicorn. It is a workhorse.