Fiddler is a Web Debugging Proxy which logs all HTTP(S) traffic between your computer and the Internet. Fiddler allows you to inspect all HTTP(S) traffic, set breakpoints, and "fiddle" with incoming or outgoing data.
Lighthouse is an open-source, automated tool for improving the quality of web pages. You can run it against any web page, public or requiring authentication. It has audits for performance, accessibility, progressive web apps, SEO and more.
GTmetrix is a free tool that analyzes your page's speed performance. Using Page Speed and YSlow, GTmetrix generates scores for your pages and offers actionable recommendations on how to fix them.
PageSpeed Insights (PSI) reports on the performance of a page on both mobile and desktop devices, and provides suggestions on how that page may be improved.
DareBoost is an online tool to test, analyze and monitor your website: speed, SEO, quality, security. All you need for website optimization in a single service.
Screpy is an AI-based web analysis tool that can analyze all pages of your websites in one dashboard and monitor them with your team. It's powered by Lighthouse and it also includes some different analysis tools (SEO, SERP, W3C, Uptime, etc).