A Laravel 11 site with Next.js 14 was running smoothly until after deploying a new feature, LCP jumped from 1.8 to 4.2 seconds and INP exceeded 300ms. The culprit — a heavy analytics script loaded without defer. This scenario is familiar to many: performance degradation often arises from subtle regressions. Our site speed optimization service focuses on fixing performance regression and improving Core Web Vitals. Our engineers with 10+ years of experience have diagnosed hundreds of such cases and brought metrics back to normal.
Identifying Typical Degradation Points
The first step is to pinpoint the time frame of the performance degradation. We use Google Search Console (Core Web Vitals over 28 days), Grafana with RUM metrics, Lighthouse CI in CI/CD, and git log. The command git log --oneline --since="2 weeks ago" --until="today" shows all deploys. If LCP increased, we cross-reference the date with commits. Once, degradation coincided with updating the swiper library — rolling back the version solved the problem in 15 minutes.
Common causes:
- JavaScript regression. Adding a script without
defer/async blocks rendering. Diagnosis: Chrome DevTools → Performance → capture trace → find tasks longer than 50ms on the main thread.
- New font without
font-display: swap. Without this, the browser hides text until the font loads, increasing LCP. Google recommends always using swap.
- Uncompressed images after CMS change. We check WebP delivery via curl:
Check WebP support with curl
curl -I -H "Accept: image/webp" https://site.ru/img.jpg | grep content-type
- CLS from elements without dimensions. Images without width/height cause layout shift. We reserve space via attributes or aspect-ratio.
Comparison of Diagnostic Tools
| Tool |
What it measures |
When to use |
| WebPageTest |
Full trace, LCP, CLS |
When suspecting image regression |
| Chrome DevTools Performance |
Main thread, long tasks |
For analyzing INP and JS tasks |
| Lighthouse CLI |
Metrics before/after |
For A/B testing changes |
| Coverage |
Unused JS/CSS |
Finding candidates for code splitting |
WebPageTest is 2x better for visual analysis than DevTools, while DevTools is 3x better for deep debugging of the critical rendering path. We combine both to precisely identify the cause of performance degradation.
Speedy Diagnosis and Common Pitfalls
Take the latest Lighthouse CI report and compare it with the previous one. If metrics dropped more than 10%, we look for regression. Use git bisect to automatically find the problematic commit. This cuts diagnosis to a few hours even in a large project. Our method is 3x faster than manual git log inspection.
A common cause of worsening metrics after updates is adding third-party scripts without considering performance. For example, a new chat widget may load 500+ KB of JS and block the main thread. We analyze every change using a performance budget in CI. If the budget is exceeded — the build fails, and performance degradation never reaches production.
How We Fix Degradation: Step-by-Step Process
- Diagnosis. Collect metrics: LCP, INP, TTFB via WebPageTest and DevTools. Analyze git log to find regression. Record database slow logs.
- Fix typical issues. Fonts, images, deferred JS loading. Saving on CDN delivery — up to 30% load time.
- Complex cases. N+1 queries, long tasks on main thread. Split into microtasks using
scheduler.yield().
- Testing. Run Lighthouse CI in parallel with production load.
- Guarantee. Provide a report with changes and a 2-week guarantee on metric restoration. If degradation recurs, we do a free re-diagnosis.
What's Included
- Diagnostic report with metric graphs
- Identification of exact regression cause
- Code, font, and image optimization
- Re-audit after fixes
- 2-week guarantee on restored metrics
- Competitive pricing: diagnosis from $500, full optimization from $1,000
Optimizing Core Web Vitals
LCP is often a large image or text block. For images, use fetchpriority="high" and preload:
Preload LCP image
<link rel="preload" as="image" href="/hero.webp" fetchpriority="high">
If LCP is text, font loading slows it down. Solution: preload the font with crossorigin and font-display: swap. Implement resource hints such as preconnect for third-party origins to reduce connection time. Use loading="lazy" for images below the fold to defer loading.
INP > 200ms means the user is waiting for a response. Typical cause: synchronous operation in a handler. We fix it by splitting into microtasks using scheduler.yield() or setTimeout(0). Learn more about yield.
If TTFB increased — the problem is on the server. Compare localhost and production via curl. If localhost is 150ms and production is 2s — issue is network or CDN. If localhost is also high — slow database query or external API.
In one project, TTFB increased from 200ms to 1.2s after adding Redis caching. It turned out cache invalidation was occurring on every request. Setting a proper TTL resolved it.
Results and Investment
| Metric |
Before |
After |
| LCP |
4.2 s |
1.5 s |
| INP |
320 ms |
180 ms |
| TTFB |
1.8 s |
0.9 s |
| CLS |
0.12 |
0.02 |
Diagnosis from $500, typical fix from $1,000, complex cases up to $3,000. Our engineers with 10+ years of experience and over 500 successful projects guarantee results. Contact us for a consultation — and we'll restore your site's speed.
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:
- Move to
<img> with fetchpriority="high" and loading="eager"
- Convert to WebP, add srcset: 800w for mobile, 1400w for desktop
-
<link rel="preload" as="image" href="hero-800.webp" media="(max-width: 768px)"> in <head>
- 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.
| Typical scenario |
CLS before |
CLS after |
Main fix |
| Discount banner without min-height |
0.42 |
0.02 |
min-height: 300px |
| Article images without attributes |
0.18 |
0.01 |
width/height + aspect-ratio |
| Chat widget loaded after 3s |
0.35 |
0.05 |
position: fixed with reserved margin |
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?
| Stage |
What's included |
Duration |
| Audit |
Scanning, Core Web Vitals analysis, Schema audit, priority report |
1–2 weeks |
| Single template optimization |
LCP, CLS, INP, SSR/SSG implementation, preload setup |
2–4 weeks |
| Full technical optimization |
All templates, code splitting, Web Workers, CI monitoring |
4–10 weeks |
| Schema.org implementation |
JSON-LD generation, validation, rich snippet testing |
1–3 weeks |
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.
