{"id":350,"slug":"lcp-killers-catalogue","title":"Reference: the 8 most common LCP killers — ranked by observed frequency","kind":"reference","scope":"business","status":"current","audiences":["claude-code","dev","candid-team"],"topics":["core-web-vitals","extractability"],"reference_body":"**Ranked by observed frequency in the field (HTTP Archive 2025 + practitioner consensus):**\n\n1. **Hero image not preloaded** and not given `fetchpriority=\"high\"`. Single largest cause. Google's own test on Google Flights: a single `fetchpriority=\"high\"` moved LCP from 2.6s to 1.9s.\n2. **Lazy-loading the LCP image** (`loading=\"lazy\"` on the above-fold hero). Common WP default since 5.5; the CMS now excludes the first 3 images, but custom themes routinely undo this.\n3. **Slow TTFB** — shared hosting with 800ms–1.5s server response; uncached dynamic queries; missing CDN.\n4. **Render-blocking CSS** — Elementor stylesheets, theme.css from heavy themes.\n5. **LCP image hidden from preload scanner** (via `data-src`, JS lazy-load libraries, CSS background-image). **Web Almanac 2025: 7% of sites still do this.**\n6. **Unoptimised image format** — JPEG/PNG instead of WebP/AVIF. WebP is 25-34% smaller than JPEG at equivalent SSIM ([[webp-25-34-smaller-than-jpeg-google-study]]).\n7. **Wrong-resolution images** — no `srcset`/`sizes`, serving 4000px desktop heroes to mobile.\n8. **Third-party scripts blocking the main document** while the LCP image waits in queue.\n\n**Remediation pattern:** Inline critical CSS → preload + `fetchpriority=\"high\"` the hero → modern image formats → `srcset`/`sizes` → move TTFB-heavy work to edge / SSG / cache. See [[rule-preload-hero-image-with-fetchpriority]].","rationale_body":null,"metadata":null,"links":{"outgoing":[{"slug":"webp-25-34-smaller-than-jpeg-google-study","title":"Google WebP Compression Study: WebP is 25-34% smaller than JPEG at equivalent SSIM (avg ~30%)","kind":"reference","scope":"business","link_type":"depends-on"},{"slug":"web-almanac-2025-cwv-pass-rates","title":"Web Almanac 2025: 48% mobile / 56% desktop origins pass all 3 CWV; LCP is the bottleneck","kind":"reference","scope":"business","link_type":"relates-to"}],"incoming":[{"slug":"rule-preload-hero-image-with-fetchpriority","title":"RULE: The LCP image always has explicit width/height + fetchpriority=\"high\" + no lazy-loading","kind":"rule","scope":"business","link_type":"depends-on"},{"slug":"research-brief-page-speed-moat","title":"Research brief: Page Speed as a Moat — why CWV separates the agencies from the freelancers (piece 9 of 15)","kind":"reference","scope":"business","link_type":"relates-to"},{"slug":"image-pipeline-avif-webp-fetchpriority-2026","title":"Candid image pipeline 2026: AVIF source / WebP fallback / JPEG last; fetchpriority=\"high\" on LCP image only; explicit dimensions always","kind":"rule","scope":"business","link_type":"relates-to"},{"slug":"renault-1s-lcp-14pp-bounce-2021","title":"Renault (2021): 1s LCP improvement → -14 ppt bounce rate, +13% conversions (regression analysis, multi-month, millions of sessions)","kind":"reference","scope":"business","link_type":"relates-to"}]},"created_at":"2026-05-22T20:03:33.375Z","updated_at":"2026-05-22T20:03:33.375Z"}