Design System Checklist
An open-source checklist to help you plan, build, and grow your design system.
While I wouldn't regard this as a silver bullet for validating your entire design system, this checklist is a really good reference point for broadly checking its health status.
I especially like that it stores the items checked in the browser's Local Storage. This means you can leave the site safely and return to it to pick up where you left off.
I also like that they're open to contributions on their GitHub repo. Wouldn't be surprised if the contributions have made that list what it is today, very comprehensive.