Lighthouse
Lighthouse is Google's free tool that audits a page on performance, accessibility, best practices, and SEO.
The tool produces a score out of 100 for each category and lists the specific issues to fix: oversized images, insufficient contrast, missing tags. It is built directly into Chrome DevTools.
Lighthouse is a starting point, not a guarantee of results: a high score does not replace real field testing. It remains the reference tool for prioritizing technical fixes before launch.