API Evangelist uses the API OAS checker from the Italian government as the validator for all API contracts. Right now it is just a stripped down static publishing of each API w/ the operational and API rules applied. The goal is to just provide a simple yet detailed accounting of governance being applied at the API and operational level.
I encourage you to download the API OAS Checker and running it locally. It has a great set of base rules and functionality that helps apply API governance to APIs, but also helps you shape your policies and rules. The default version of the API OAS Checker has some more capabilities, and is very easy to customize and publish to run via GitHub, or anywhere you can host static site.