Is it working?
This page does not tell you the site is fine. It runs the actual analysis engine against four known files in your browser, right now, and shows you what came back — including one deliberate forgery it has to refuse.
This check needs JavaScript. That is also true of the tool itself — all the work happens in your browser.
Nothing on this page is sent anywhere. The four test files ship with the page and are the same ones the automated test suite uses, so this cannot claim a check that is not really made.