The best open source alternative to Yahoo! YSlow is Google Lighthouse. If that doesn't suit you, our users have ranked more than 10 alternatives to Yahoo! YSlow and four of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Yahoo! YSlow are PageSpeed Insights, WebPageTest and Yellow Lab Tools.
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.
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.
Run a free website speed test from around the globe using real browsers at consumer connection speeds with detailed optimization recommendations.
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