Website performance: a full Lighthouse audit in 30 seconds
You just shipped a fresh landing page and want to make sure it isn't heavy as a brick. A client asks why their store takes 9 seconds to load. You are pitching a redesign and need a number on the slide ("they score 38, you'll be at 95"). All these situations share one answer: a Lighthouse audit.
This tool asks the Google PageSpeed Insights API (the same Lighthouse engine Google Search Console uses) for the full report: four 0-100 scores (Performance, Accessibility, Best Practices, SEO), Core Web Vitals (LCP, INP, CLS, FCP, TTFB, Speed Index) and a list of concrete things to fix (e.g. "this 1.2 MB hero image blocks rendering, you can save 2.8 s").
Where does the data come from? The lab measurement runs in Google's cloud on a simulated 4G connection plus mid-tier smartphone. If the site has real-user data in the Chrome User Experience Report (CrUX) - Google's public dataset of field metrics from real Chrome visitors - then INP and TTFB include that field data. Smaller sites usually have no CrUX sample, so you only see the lab numbers.
Mobile vs Desktop: not the same audit. Mobile throttles to a Moto G4-class device on a slow 4G (1.6 Mbps, 150 ms latency), so scores are always lower. Google prioritises mobile in its ranking (mobile-first indexing since 2019), so check that first.
How to use it
- Paste the URL of the page you want to audit. You can skip `https://`, we will add it. It must be a public URL - Google cannot reach `localhost`, `.local`, or pages behind a login.
- Pick a strategy: Mobile (default, what matters for SEO) or Desktop (easier to hit 90+, useful for comparison). Audit both when the quota allows - mobile is often dramatically slower.
- Click Run check and wait 10-30 seconds. Google literally loads the page in a virtual browser, measures every step and scores it. This is not a cached lookup - every run is a fresh measurement.
- You see 4 dials (Performance, Accessibility, Best Practices, SEO). Green = 90-100, amber = 50-89, red = 0-49. Google considers green as "good", the rest is room to improve.
- Below the dials are the Core Web Vitals: LCP (Largest Contentful Paint, when the screen visually looks ready), INP (Interaction to Next Paint, how fast the page responds to clicks), CLS (Cumulative Layout Shift, whether content jumps while loading), FCP, TTFB, Speed Index.
- The opportunities list at the bottom is the actionable bit - concrete fixes sorted by impact. Each shows estimated savings, e.g. "compress images: -2.1 s". Tackle the first 3 marked High, the rest is small print.
- Re-run after deploying a fix: new measurement, new score, easy comparison. Open in PageSpeed Insights sends you to the official Google report on pagespeed.web.dev (same data, more detail).
When this is useful
Six situations where this tool beats a verbal "should be fast enough":
- Pre-deploy regression check. You just did a big frontend refactor (framework update, new component library, CMS swap). Before pushing to production, you confirm the score did not drop below 90. If it did - you know to dig into what was added (usually: an oversized JS bundle or unoptimised images).
- Showing a competitor to a client. Sales meeting. You want to prove the client's current vendor ships slow sites. You audit their page and a competitor's: 38 vs 92. The client starts listening - Google's numbers are hard to argue with.
- Diagnosing "why is the shop slow". A client says conversion dropped and they suspect speed. You audit: LCP 6.8 s (should be under 2.5 s), opportunities show "hero images too large (3.4 MB)". Fixed in half a day.
- SEO audit before a migration. The client is moving from WordPress to Shopify / Webflow / a custom stack. You audit the current site before and the new site after, comparing all 4 scores. SEO tells you whether meta tags, alt text and sitemap survived. Best Practices - whether you introduced mixed content or deprecated APIs.
- Validating a hosting / CDN change. You move from a generic VPS to Vercel / Cloudflare Pages / Netlify. Audit mobile + desktop before and after. TTFB (Time To First Byte) shows immediately whether the server responds faster. LCP - whether images load faster (CDN cache hit).
- WCAG accessibility spot-check. Public-sector or compliance-driven clients need WCAG 2.1 AA conformance. The Accessibility audit covers contrast, alt text, ARIA roles, focus rings. A full audit needs human review, but Lighthouse catches around 80% of the technical issues.
Need more context? The SSL certificate inspector confirms HTTPS is correctly configured (a prerequisite for Best Practices = 100). The DNS lookup shows whether the server responds via the right records. The Open Graph preview helps verify the social-share meta tags Lighthouse expects you to set.