API Evangelist uses the API OAS checker from the Italian government as the validator for all API contracts. I publish an instance dedicated to the APIs.json for any API I am reviewing, providing a good way to show the homework behind any review, and make it so you can edit the APIs.json along the way to get the results you want.
The Business Contract Validator is just a static build of the APIs.json for an API at any point in time, and I will add editing, versions, and other capabilities. Right now the goal is to just be able to think about the shape of governance, as well as how it impacts a single API, or many different APIs. I am working on a suite of APIs that will be extending the capabilities available via the validator.