Lighthouse Score Simulator - Estimate Core Web Vitals & Performance Scores

It's important to be direct about what this tool is and isn't. The scores here are synthetic estimates, generated from a simplified heuristic model - they are not measured by rendering your actual page, and they will not match what Lighthouse, PageSpeed Insights, or Chrome DevTools report for a real URL.

• No real page is fetched, rendered, or executed - your URL field is for reference/labeling only
• Metrics are derived from sliders you set (JS size, image size, third parties, CPU slowdown), not from actual network or script analysis
• Random jitter is added between runs to simulate real-world score variability, not measured variance
• Real Lighthouse scores also depend on factors this tool doesn't model: server response time (TTFB), actual render-blocking resources, real font-loading behavior, and more
• For an authoritative score, always run Lighthouse in Chrome DevTools or PageSpeed Insights against the live URL

Google's three Core Web Vitals - Largest Contentful Paint, Interaction to Next Paint, and Cumulative Layout Shift - remain the field-data metrics Google uses to judge real-world page experience. A page passes Core Web Vitals only when at least 75% of real visits, measured over a rolling 28-day window in the Chrome User Experience Report (CrUX), meet the "good" threshold for all three metrics simultaneously.

INP officially replaced First Input Delay (FID) as the responsiveness metric in March 2024 and remains in place in 2026. Where FID only measured the delay before the very first interaction, INP evaluates the full latency of every interaction across the page's lifetime, making it a considerably stricter and more representative test - and, per recent field data, the Core Web Vital most sites currently fail.

Core Web Vitals are a confirmed ranking signal, but function primarily as a tie-breaker between pages of otherwise similar relevance and quality - not a factor that overrides strong content. Their larger, better-documented impact is on conversion: faster, more stable pages measurably reduce bounce rate and improve engagement independent of any SEO effect.

Even a real Lighthouse audit only produces lab data - a single test run in a controlled environment. Google's ranking-relevant Core Web Vitals assessment is based on field data from the Chrome UX Report: real measurements from real Chrome users on real devices and networks, aggregated at the 75th percentile over 28 days.

A perfect Lighthouse score on your development machine means little if a quarter or more of your real visitors - often on mid-range phones or slower connections - experience something much worse. This is exactly why this simulator lets you explore multiple device and throttling scenarios rather than showing a single fixed number: real-world performance is a distribution, not a point estimate.