WebPageTest

WebPageTest measures how a web page loads in real browsers, from a chosen test location, device and connection type. A test produces a request waterfall, a filmstrip and video of the page rendering, Core Web Vitals and detailed timings for DNS, TCP, TLS and each resource, so that slow requests and render-blocking resources can be identified.

The project was created and open-sourced by Patrick Meenan in 2008. It is now maintained by Catchpoint, part of LogicMonitor. The code that runs webpagetest.org is published on GitHub under the Polyform Shield licence, and it can be installed as a private instance with its own test agents.

Tests can be run for free on webpagetest.org, with a free account required for the full set of options. Paid plans add features such as a developer API, experiments, scheduled monitoring and real user monitoring.