It fetches the page and scans its raw HTML for six structural issues: images with no alt attribute, links and buttons with no visible text or accessible label, form fields with no associated label, a missing <html lang> attribute, a missing <title> tag, and heading levels that skip a step (like H2 straight to H4). Each category is reported with its own count and a capped scoring deduction, plus a detail list of the individual elements found.
How to fix what it finds
Add a meaningful alt attribute to every content image (or an empty alt="" if it's purely decorative), give every link and button real visible text or an aria-label, pair every form field with a proper <label for="...">, set lang on your <html> tag, and fix your document outline so headings step down one level at a time. None of these require JavaScript or a redesign — they're all one-line template fixes.