GTmetrix

GTmetrix is an online service that tests how fast a web page loads and explains what slows it down. Its reports are based on Lighthouse and include Web Vitals (LCP, TBT, CLS), structure audits, a request waterfall, a video and a filmstrip of the page load.

Tests can be run from 28 locations and with simulated mobile and tablet devices, and the connection speed, user agent, screen resolution and cookies can be set. Real user data from the Chrome UX Report (CrUX) is shown next to the lab results.

The service has been available since 2010. A free test is available without an account. Paid plans add scheduled monitoring with alerts, more locations and test options, an API and an MCP server for AI agents.