Free Performance Tool

PageSpeed & Core Web Vitals Checker

Check Core Web Vitals, get AI-powered fix code. LCP root cause analysis, third-party impact, competitor comparison.

Last updated: April 2026

How This PageSpeed Checker Works

This tool calls Google's PageSpeed Insights API and does something no other speed tool does: it turns the raw Lighthouse data into copy-ready fix code. When Google says "eliminate render-blocking resources", this tool shows you exactly which scripts are blocking, estimates the time savings, and generates the actual preload tags or async attributes you need.

Every test runs both mobile and desktop in parallel. You see four Lighthouse category scores, six lab metrics with Good/Warning/Poor badges, CrUX field data when available, and an LCP root cause breakdown that traces your loading time from server response to final render. The AI Fix Engine then reads the full audit data, detects your tech stack, and generates prioritized fixes specific to your platform.

What Are Core Web Vitals?

Three metrics that Google uses as ranking signals since 2021. LCP (Largest Contentful Paint) measures loading speed: your hero image or main heading should appear within 2.5 seconds. INP (Interaction to Next Paint) measures responsiveness: clicks and taps should produce a visual response within 200ms (150ms since the March 2026 Core Update). CLS (Cumulative Layout Shift) measures visual stability: elements shouldn't jump around as the page loads, target below 0.1.

Why LCP Phase Breakdown Matters

Your LCP score is a symptom. The four phases behind it are the diagnosis. A 3-second LCP caused by slow TTFB (server issue) needs a completely different fix than one caused by a massive hero image (asset issue) or render-blocking JavaScript (delivery issue). Most speed tools show you the final number. This one shows you where the time actually goes, so you fix the right thing first.

How to Improve Your PageSpeed Score

Four levers handle 80% of speed problems. Optimize your LCP element (usually the hero image) by converting to AVIF or WebP and adding a preload tag. Defer render-blocking JavaScript and inline critical CSS. Reserve space for images with explicit width/height to kill layout shift. Enable Brotli compression to cut transfer sizes by 70%. Most sites go from "needs improvement" to "good" with just these four changes.

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FAQ

What makes this different from Google PageSpeed Insights?+

Google PSI shows what's wrong but not how to fix it. This tool adds three things: AI-generated fix code you can copy and paste, an LCP root cause breakdown that traces loading time across four phases, and deep analysis panels for render-blocking resources, third-party impact, unused code, and CLS elements.

How does the competitor comparison work?+

Click "+ Compare" and enter a competitor URL. Both sites get tested in parallel on the same Google infrastructure. You see your scores side by side with delta values showing where you lead and where you trail. Same test conditions, direct comparison.

Is this free?+

Yes. The PageSpeed Insights API is free. The AI fix engine has a daily credit limit which you can bypass by adding your own OpenAI API key in Settings.

What are Core Web Vitals?+

Three metrics Google uses as ranking signals: LCP measures loading speed (target under 2.5s), INP measures responsiveness (target under 200ms, lowered to 150ms since March 2026), and CLS measures visual stability (target under 0.1).

Why is my mobile score lower than desktop?+

Lighthouse simulates a mid-tier phone on a throttled 4G connection for mobile tests. Desktop uses a faster profile. Real mobile performance is almost always worse than desktop because of CPU throttling and network constraints. Google uses mobile-first indexing, so the mobile score is the one that matters for rankings.

PageSpeed data in every audit

Lumina integrates PageSpeed testing directly into the Chrome extension.

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