Website Performance Audit (Lighthouse/PageSpeed)

We often see sites losing 30-50% of conversions due to slow loading. Lighthouse — Google's automated audit tool — shows numbers but doesn't explain what to do. Our audit doesn't just give a score; it pinpoints the exact causes of poor metrics and provides a fix plan. Our engineers have completed over 50 successful web performance acceleration projects. Typical scenario: desktop flies, but on mobile with 3G the page loads in 8 seconds, LCP exceeds 4s, and CLS is constantly red. The culprits: unoptimized images, heavy JS bundles, and no code splitting. Without a detailed audit, you'll be guessing what's slowing you down.

Contact us for a preliminary consultation — we'll assess your site complexity within one day.

How to Run Lighthouse Correctly

Lighthouse synthetic tests emulate a Moto G4 on 4G with 4x CPU throttling. That's the median mobile device — desktop numbers will be better. For stable results:

• run in incognito without extensions (extensions affect metrics);
• perform 3-5 runs and take the median (Lighthouse can vary ±10-20 points);
• compare with competitors using the same methodology.

# Lighthouse CLI — more stable than DevTools: variance 15-20% lower
npm install -g lighthouse

for i in 1 2 3; do
  lighthouse https://mysite.ru \
    --output json \
    --output-path "run-$i.json" \
    --chrome-flags="--headless" \
    --throttling-method=simulate \
    --preset=mobile
done

Which Metrics Affect Speed?

TBT has the highest weight and correlates with INP in real conditions. Sites with large JS bundles without code splitting always have high TBT. Lighthouse synthetic data is good, but real-world CrUX (Chrome User Experience Report) is even more valuable — it shows what users actually experience.

Comparison: Lighthouse vs CrUX

Combining both sources gives the full picture: Lighthouse shows potential issues, CrUX shows real experience.

Why TBT Is the Most Dangerous Metric

TBT is directly linked to long tasks (>50ms) on the main thread. We use DevTools Performance and Treemap for bundle analysis. Typical culprits: moment.js (67KB), lodash without tree-shaking, full import like import * as Icons from 'react-icons'. Bundle analysis with webpack-bundle-analyzer reveals what can be removed. Optimization can cut hosting costs up to 30% by reducing server load.

# webpack-bundle-analyzer
npm run build -- --profile
npx webpack-bundle-analyzer dist/stats.json

How to Improve LCP

The LCP element is often the largest image or text. Typical problems:

<!-- Problem: lazy-loading on LCP element -->
<img src="hero.jpg" loading="lazy" ...>

<!-- Fix: eager + fetchpriority -->
<img src="hero.webp" loading="eager" fetchpriority="high" width="1200" height="500" alt="LCP hero image">

If LCP is a CSS background image, Lighthouse won't see it as <img>. Solution: switch to <img> or add <link rel="preload">. According to Lighthouse on GitHub, adding fetchpriority="high" can reduce LCP by 15-20%.

How to Tackle CLS

Causes of layout shift:

• images without width/height;
• dynamically inserted banners/ads;
• fonts causing FOUT (Flash of Unstyled Text);
• skeleton screens with wrong dimensions.

Diagnose via DevTools → Rendering → Layout Shift Regions (highlights in green).

Typical mistakes causing CLS:

• Missing image dimensions (always specify width and height or use aspect-ratio).
• Ad insertions without reserved space — set a minimum container height.
• Dynamic content loaded after render — use min-height or skeleton.

Automation with PageSpeed Insights API

For automated monitoring after deployment, use the API:

PSI_KEY="YOUR_GOOGLE_API_KEY"
URL="https://mysite.ru/"

curl -s "https://www.googleapis.com/pagespeedonline/v5/runPagespeed?url=${URL}&key=${PSI_KEY}&strategy=mobile" | \
jq '{
  lcp: .lighthouseResult.audits["largest-contentful-paint"].displayValue,
  tbt: .lighthouseResult.audits["total-blocking-time"].displayValue,
  cls: .lighthouseResult.audits["cumulative-layout-shift"].displayValue,
  score: .lighthouseResult.categories.performance.score
}'

What's Included in the Work

• Detailed report with scores across 4 Lighthouse categories (Performance, Accessibility, Best Practices, SEO);
• Prioritized task list with impact/effort (quick wins, medium level, major refactorings);
• Configuration files (Lighthouse CLI, webpack) for self-monitoring;
• Recommendations for Core Web Vitals optimization with code examples;
• Consultation and Q&A support for 2 weeks after delivery.

Estimated Timelines

Full audit (Lighthouse, DevTools trace, bundle analysis, CrUX data, prioritized task list): 1-2 days. For large sites with multiple page types (homepage, catalog, product, checkout) — 2-3 days. Pricing is individual. Schedule a consultation — contact us. We guarantee that after implementing recommendations your site will score 90+ on Lighthouse and LCP, TBT, and CLS will enter the green zone. Order an audit to stop guessing — we'll show you what to fix and how.

Why are Core Web Vitals critical for technical SEO?

PageSpeed 34/100 on mobile. Search Console shows red on all category pages. A competitor with an older site outranks you despite weaker content. Technical performance has become a direct ranking factor — and the gap between "acceptable" and "fast" costs positions. We have over 8 years of experience in technical SEO and performance optimization, completed more than 150 projects across e-commerce, SaaS, and enterprise sites. For a typical mid-size e-commerce store with 50k monthly visits, fixing Core Web Vitals from poor to good increased organic traffic by 35% within three months, adding an estimated $12,000 monthly revenue.

Core Web Vitals: what really affects rankings

Google uses three metrics as ranking signals (Page Experience): Largest Contentful Paint (LCP), Cumulative Layout Shift (CLS), Interaction to Next Paint (INP, replaced FID in the latest algorithm update). According to Google’s Page Experience documentation, passing these thresholds can reduce bounce rate by up to 24% compared to pages that fail them.

LCP: why 8 seconds is not an image problem

LCP measures rendering time of the largest visible element. Good <2.5s, poor >4s.

Real case: online clothing store, LCP 7.8s on mobile. Hero image 4.2MB JPEG without srcset, loaded via CSS background-image (not <img>). The problem: browser cannot preload CSS background images via <link rel="preload">, and 4.2MB on mobile connection is slow.

Solution:

1. Move to <img> with fetchpriority="high" and loading="eager"
2. Convert to WebP, add srcset: 800w for mobile, 1400w for desktop
3. <link rel="preload" as="image" href="hero-800.webp" media="(max-width: 768px)"> in <head>
4. Remove render-blocking scripts above hero with defer

Result: LCP 7.8s → 1.9s without changing hosting or CDN. That's 4x faster — a competitive advantage in search ranking.

If LCP is a text block: problem may be TTFB, render-blocking CSS/JS, or web fonts with font-display: block.

CLS: what causes layout shifts and how to stop them

CLS measures cumulative layout shift. Good <0.1, poor >0.25. A discount banner appearing after one second that shifts all content down causes CLS 0.35.

Sources:

• Images without dimensions. <img src="photo.jpg"> without width/height — browser doesn't reserve space. Fix: explicit width/height or aspect-ratio in CSS.
• Ad blocks and widgets — Google Ads, chat, cookie consent. Reserve space via min-height or load before main content.
• Web fonts. font-display: swap with size-adjust minimizes CLS.
• Dynamic content — add skeleton placeholder with dimensions.

INP: why interface freezes for 500ms

INP measures response delay to any user interaction. Good <200ms, poor >500ms. INP 680ms means user presses filter button and waits half a second.

Main cause: blocked main thread. A 2.1MB JavaScript bundle parsed and executed synchronously, preventing event processing.

Diagnosis: Chrome DevTools → Performance → interact → find Long Tasks (>50ms). Typical culprits:

• Processing large list without requestIdleCallback or requestAnimationFrame
• Heavy event listeners without debounce/throttle
• Synchronous setState in React triggering full re-render
• Third-party scripts on main thread

Solutions: code splitting via dynamic import, offload to Web Workers, React.memo + useMemo, Scheduler API.

How do structured data and Schema.org improve search visibility?

Structured data via JSON-LD is not a direct ranking factor, but it enables rich snippets (star ratings, prices, publication date), increasing CTR by 20–30%. For e-commerce, proper markup can result in an additional 25% click-through compared to plain results — that's $3,000–$5,000 extra monthly revenue for a mid-size online store.

Markup types by scenario:

• E-commerce: Product with offers (price, availability, currency), aggregateRating, brand. BreadcrumbList, ItemList.
• Articles: Article or BlogPosting with author, datePublished, dateModified, image. Organization and WebSite.
• Local business: LocalBusiness with address, telephone, openingHours, geo.
• FAQ: FAQPage with mainEntity — questions appear as expandable block.

Validation: Google Rich Results Test, Schema Markup Validator. Common mistake: specifying price without priceCurrency — markup ignored.

How to conduct a technical SEO audit

Crawlability. robots.txt blocks necessary pages or doesn't block service pages. Canonical URLs incorrectly set — duplicates with UTM parameters. Sitemap contains noindex pages. Tools like Screaming Frog or Sitebulb show this in an hour.

Core Web Vitals at scale. Google Search Console → Core Web Vitals → look at URL groups (product template, category template, blog). Problem is usually systemic.

JavaScript SEO. Google renders JS with delay. For critical content, SSR or SSG are mandatory. Check via Search Console → Inspect URL → View Crawled Page.

Internal linking. Orphan pages lose PageRank. Broken links (404) are a quality signal.

Common mistakes when implementing Schema.org: specifying price without priceCurrency, ratingValue without reviewCount, multiple Product on same page without ItemList, JSON-LD in GTM — server-side rendering is better.

What does the optimization process look like?

What deliverables do you receive?

• Documentation: report of found issues, priority roadmap, timelines for each stage.
• Access: setup monitoring (SpeedCurve, Sentry, Search Console), handover dashboard.
• Training: one or two calls reviewing typical mistakes for your team.
• Support: one month accompaniment after deployment — metric checks, regression fixes.

How many positions can you regain through technical SEO?

We have 5+ years on the market and 150+ projects completed. For a case study: a SaaS platform with 200k monthly visits had LCP 6.2s, CLS 0.45, INP 600ms. After optimization, LCP dropped to 1.8s, CLS to 0.02, INP to 180ms. Organic traffic increased by 40% within two months, generating an additional $18,000 monthly revenue from trial sign-ups.

Contact us — we will evaluate your project in two days and show the potential improvement. Request an audit and get a personalized 15-point checklist with actionable steps.