toolsPublished26.05.2026

WebPageTest

WebPageTest is a free tool for testing website load speed. It displays a detailed waterfall chart, Core Web Vitals, TTFB, and performance optimization recommendations.

In brief

WebPageTest is an open-source online service for measuring web page performance. It tests with a real browser on a real connection, providing a request waterfall diagram, Core Web Vitals, TTFB, Speed Index, and other load metrics.

What is WebPageTest

WebPageTest is a free, open-source tool for testing web page load speed, developed by Catchpoint. Testing runs with a real browser (Chrome, Firefox, Edge) from a chosen geographic location — which is its main differentiator from synthetic tools.

The test result is a detailed report: a waterfall diagram of all network requests, Core Web Vitals metrics, a filmstrip view of the page loading, screenshots, and a video recording. Frontend developers and SEO specialists use it to diagnose performance issues.

WebPageTest lets you configure connection throttling (3G, 4G, cable), device type (desktop/mobile), number of runs, and first/repeat view — making the test as close to real user conditions as possible.

Key WebPageTest metrics

TTFB (Time to First Byte)
Time from request to receiving the first byte of the server response. Target: < 600 ms.
First Contentful Paint (FCP)
Time until the first content appears on screen. Target: < 1.8 sec.
Largest Contentful Paint (LCP)
Time until the largest visible element is loaded. Good: < 2.5 sec.
Total Blocking Time (TBT)
Total time the main thread is blocked between FCP and Time to Interactive. Correlates with INP.
Speed Index
How quickly the visible part of the page fills visually. Lower is better.
Fully Loaded
Time until the full page, including all resources, is loaded.

Waterfall diagram

The waterfall is the primary diagnostic tool in WebPageTest. It is a timeline of all network requests for the page: HTML, CSS, JS, fonts, images, API calls.

  • Each row is one request. Color indicates resource type
  • Bar length = load time. Shows DNS lookup, TCP connection, TTFB, and download phases
  • Parallel rows = browser loading multiple resources simultaneously
  • Render-blocking resources appear as requests that stall page rendering
  • Vertical lines mark key metrics (FCP, LCP, Load Event)

WebPageTest vs. PageSpeed Insights

ParameterWebPageTestPageSpeed Insights
Test typeReal browserLighthouse (synthetic) + CrUX (field)
LocationChoose from 40+ locationsFixed
WaterfallYes — detailedNo
Load recordingYesNo
Core Web VitalsYesYes
CostFreeFree
APIPaidFree

How to use WebPageTest for SEO

  1. Enter the page URL and choose a test location closest to your target audience
  2. Set realistic throttling: 4G for mobile testing, cable for desktop
  3. Run 3–5 test runs to get an averaged result
  4. Study the waterfall: find render-blocking resources, large JS bundles, slow TTFB
  5. Use Opportunities & Experiments — built-in advice with estimated impact
  6. Save the result URL: it's permanent and useful for before/after comparison
FAQ

Common questions

WebPageTest tests with a real browser and shows a waterfall and load video recording. PageSpeed Insights runs Lighthouse (synthetic) and additionally shows real-world data from the Chrome User Experience Report. For diagnosing specific issues, WebPageTest is more informative.
After every major change (redesign, new scripts, hosting migration). For ongoing monitoring — weekly, or via API/CI integration on every deploy.
Yes. Select 'Moto G (gen 4)' as the device and 4G throttling. This is the standard configuration for mobile performance testing, closely approximating real user conditions.
A built-in recommendation system that automatically suggests optimizations with an estimated LCP improvement. The 'Experiments' mode applies the optimization and shows the result immediately — without changing any code.
Direct contacts

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