Allows scanning a website for different performance characteristics. There are five test kinds: 1) Site Performance, 2) Core Web Vitals, 3) Lighthouse, 4) Visual Comparison, and 5) Traceroute. It reports many web performance problems, like download times, first paints or problems with mobile devices.

https://pagespeed.web.dev/

Reports basic web performance data for mobile and desktop browsers.

Web Performance Testers

https://www.webpagetest.org/

https://pagespeed.web.dev/