GTmetrix

What it does

GTmetrix is a website performance testing tool built on Google Lighthouse that measures Core Web Vitals (Largest Contentful Paint, Total Blocking Time, Cumulative Layout Shift) and generates detailed waterfall charts, video playback of page loads, and prioritized recommendations for speeding up a page. Tests can be run from over 20 global locations and across 40+ device profiles to see how load times vary by region and device. Paid plans add scheduled monitoring with hourly checks and alerts, more daily tests, and an API for automating performance checks into a CI/CD pipeline. The free tier is sufficient for occasional one-off diagnostics but not for ongoing monitoring.

Who this helps

• Developers and site owners diagnosing exactly which resource (script, image, font) is slowing down a page load.

• Agencies running pre-launch performance checks before handing a site off to a client.

• Technical SEOs who need Core Web Vitals data with more visual detail than Google PageSpeed Insights provides alone.

• Teams that want scheduled, automated performance monitoring with alerts when a page regresses (paid tiers only).