Website Speed Test

A slow website costs conversions, rankings, and user patience in equal measure. Google's Core Web Vitals are now ranking signals, and even a half-second improvement can lift organic traffic measurably. This speed test runs a real performance audit on any public URL and reports Core Web Vitals, a performance score, resource breakdown, and specific recommendations prioritized by impact.

The audit measures Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS) — the three current Core Web Vitals. It also measures classic metrics like First Contentful Paint, Time to First Byte, Total Blocking Time, and Speed Index. Each metric is scored against Google's thresholds (good, needs improvement, poor) so you know where to focus.

Beyond the metrics, the tool provides a resource waterfall showing what loaded when and how long each request took. Render-blocking CSS and JS are highlighted, unused code is flagged, unoptimized images are called out with suggested formats and sizes, and third-party scripts (analytics, chat widgets, ads) get their own impact assessment. Every recommendation includes an estimated savings in milliseconds and a plain-English explanation of how to fix it. Run the test on desktop and mobile network profiles to understand the user experience across devices, and export the report to share with your dev team or stakeholders.

Website speed tests use a headless browser (Chrome DevTools Protocol) to load your page under controlled network and CPU conditions, then collect the metrics browsers expose through the Performance API. The core metrics tracked:

- LCP (Largest Contentful Paint): time until the largest above-the-fold element renders. Target: under 2.5s. Often an image or hero text block.
- INP (Interaction to Next Paint): perceived responsiveness during interactions (clicks, taps, key presses). Replaced FID in March 2024. Target: under 200ms.
- CLS (Cumulative Layout Shift): sum of all unexpected layout shifts during page load. Target: under 0.1. Often caused by images without dimensions or injected ad slots.
- TTFB (Time to First Byte): server response latency. Target: under 800ms. Indicates hosting or CDN quality.
- FCP (First Contentful Paint): time until first text or image renders. Target: under 1.8s.
- TBT (Total Blocking Time): time main thread was blocked during load. Target: under 200ms.
- SI (Speed Index): how quickly above-the-fold content visually populates. Target: under 3.4s.

The tool runs the audit with a simulated slow 4G network profile and mid-tier mobile CPU to approximate real-world conditions (per Google's mobile-first approach). Desktop tests use faster network and CPU assumptions. Results include a lighthouse-style score (0-100 per category) combining all metrics.

Recommendations come from analyzing the resource waterfall. Large images are flagged with suggestions for WebP/AVIF conversion. Render-blocking JS is identified for async/defer/module loading. Unused CSS in above-the-fold selectors suggests critical CSS extraction. Third-party scripts get individual impact assessments so you can weigh features against performance. Exports include HTML, JSON, and CSV formats for tracking improvements over time.

Google PageSpeed Insights is the reference test but runs on Google infrastructure and isn't always available for every URL. GTmetrix offers good analysis but gates features behind a paid tier. WebPageTest is powerful but has a steep learning curve. This tool uses the same Lighthouse engine, surfaces Core Web Vitals prominently, adds prioritized recommendations with savings estimates, and runs in the browser — no account, no queuing, no limits. Pair with Chrome DevTools Performance tab for deep investigation.