PageSpeed Analyzer: Measure and Fix Your Google Lighthouse Score
Every second of load time costs conversions. Google''s own research shows that as page load time increases from one to five seconds, the probability of a mobile visitor bouncing increases by 90%. Yet most teams only discover their PageSpeed score the day a stakeholder runs a Lighthouse audit and shares a screenshot of a red "32". This tool puts a continuous, zero-setup Lighthouse runner in your browser so you can check any URL in seconds and understand exactly what the score means.
What Is Google Lighthouse and Why Does It Matter?
Google Lighthouse is an open-source automated auditing tool built into Chrome DevTools and powering the PageSpeed Insights API. It simulates a mid-tier Android device on a throttled 4G connection, loads your page, and measures six performance metrics. From those metrics, it calculates a single weighted Performance Score from 0 to 100.
Since June 2021, Core Web Vitals — a subset of Lighthouse metrics — are an official Google ranking factor. A poor mobile Lighthouse score is therefore not just a UX problem; it is a direct SEO liability.
The Six Lighthouse Metrics and Their Weights
| Metric | Weight | What it measures |
|---|---|---|
| First Contentful Paint (FCP) | 10% | Time until the first DOM content renders |
| Speed Index (SI) | 10% | How quickly the visible area populates |
| Largest Contentful Paint (LCP) | 25% | Time until the largest visible element renders |
| Total Blocking Time (TBT) | 30% | Milliseconds of main-thread blocking during load |
| Cumulative Layout Shift (CLS) | 15% | Visual instability from elements moving during load |
| Time to Interactive (TTI) | 10% | Time until the page is reliably interactive |
TBT has the highest weight at 30%. This surprises teams that focus exclusively on network metrics. TBT is dominated by JavaScript execution — long tasks that block the main thread and make the page feel frozen even after it visually loads. Every JavaScript bundle you ship contributes to TBT.
This tool surfaces FCP, LCP, and Speed Index — the three metrics with the strongest correlation to perceived load speed and the easiest to understand without deep Lighthouse expertise.
Google''s Threshold System: Good, Needs Improvement, Poor
Each Core Web Vital has three performance ranges:
First Contentful Paint
- Good: ≤ 1.8 s
- Needs improvement: 1.8–3.0 s
- Poor: > 3.0 s
Largest Contentful Paint
- Good: ≤ 2.5 s
- Needs improvement: 2.5–4.0 s
- Poor: > 4.0 s
Speed Index
- Good: ≤ 3.4 s
- Needs improvement: 3.4–5.8 s
- Poor: > 5.8 s
The Eight Most Common Causes of Low Lighthouse Scores
1. Unoptimised hero images — A 2 MB JPEG hero can push LCP past 6 seconds on a throttled connection. Use next/image, WebP/AVIF, and explicit dimensions.
2. Render-blocking scripts — Synchronous <script> tags in <head> halt HTML parsing. Add defer or async.
3. Excessive JavaScript bundle size — Every kilobyte must be parsed and compiled. Code-split with dynamic imports and audit third-party payloads.
4. No CDN — A 150 ms round-trip to origin adds up fast across 20+ requests. Use Vercel, Cloudflare, or similar.
5. Missing Cache-Control headers — Without caching, every visit re-downloads unchanged assets.
6. Web font blocking — No font-display: swap or missing <link rel="preload"> delays FCP by seconds.
7. Heavy third-party scripts — Analytics, chat widgets, and A/B tools are leading TBT contributors.
8. Client-only rendering — SPAs without SSR shift FCP to after JavaScript execution. Use Next.js or Nuxt.
How Vector Input Achieves 100/100
Every site we build ships with performance as a requirement, not an afterthought: React Server Components, automatic image optimisation, Vercel Edge Network, font subsetting, bundle budget gates on CI, and third-party script isolation via Partytown.
If your site scored below 90, request a free technical audit — we will identify every bottleneck and deliver a prioritised remediation plan.
Interpreting Your Score
90–100 (Green) — Performing well. Monitor Core Web Vitals in Search Console for regressions.
50–89 (Orange) — Meaningful issues. Focus on image optimisation and JavaScript bundle size first.
0–49 (Red) — Significant problems affecting rankings and conversions. Immediate action recommended.