Pingdom web site monitoring and other infrastructure for you and instantly let you know when anything goes wrong. Measure uptime, downtime, and the performance of your website as experienced by visitors.
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.
HTTP Toolkit is a beautiful, cross-platform & open-source HTTP(S) debugging proxy, analyzer & client, with built-in support for modern tools from Docker to Android to GraphQL.
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.