WebPageTest
webpagetest.org
A free web performance testing tool that runs your site from real browsers in real locations, producing detailed waterfall charts, Core Web Vitals, and optimization recommendations.
Why it is useful
The most detailed free performance testing tool available — the waterfall charts identify exactly which resources are blocking render and where time is being lost, rather than just a score. Running tests from real browsers in specific geographies gives a realistic picture of what users actually experience. The filmstrip view of page loading is especially useful for diagnosing visual performance issues.
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