I built an Hreflang testing tool. https://app.hreflang.org

Hreflang is an arcane SEO concept. If you have sites in different languages then you can tell Google/Bing that site.com/page.html and site.fr/page.html are basically the same page only in diff languages.

The way to specify this is using meta tags in your HTML, and it's quite complex and error-prone. My tool checks if you implemented this correctly. It's running on a VPS so my cost is quite low.