Maybe one day, JSON Schema would be able to express all the constraints in the OpenAPI spec, but I suspect some are going to be really hard.

When we do release a final version of JSON Schema, please do not use JSON Schema to guarantee an OpenAPI document is valid. It cannot do that. There are numerous constraints in the written specification that cannot be expressed in JSON Schema.

Another big issue is that the config wasn’t really expressive enough. From the beginning Rails needed a way to say “only compile application.css and application.js, but compile ALL images” by default. With our previous interface, we’re limited to only strings.