There has been a lot of recent work on making a valid JSON Schema available for the JSON:API spec.

For the 1.0 spec, #1600 was merged, but it doesn't seem quite complete. The schema in that PR is not publicly-available and it also deleted the old schema available at /schema. It was committed without any comment from @dgeb so I'm not sure if there was a follow-up intended here.

PR #1603 would add a 1.1 spec, and was blocked on the validation code added in #1600 but that's no longer an issue.

Issues like #1743 are cropping up about the missing schema. Indeed, I'm working on a schema generation issue for a library and it's difficult to debug it end-to-end since the linter can't load the JSON:API schema.

I would propose that /schema be a copy of the most up-to-date spec (that would be 1.1 when that PR is ready) and also the published schemas have an $id that maps to a routable URL.