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Crawlmind
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Rule page.performance.lcp-slow

Improve Largest Contentful Paint (LCP)

page.performance.lcp-slow is a check in Crawlmind's site audit that grades high-impact issues of this kind. This page explains why the rule matters and the exact fix.

Impact: highEffort: high

Why it matters

LCP measures when the largest above-the-fold element finishes rendering. Google's "good" threshold is under 2.5s at the 75th percentile of real users. Past it, rankings suffer (Core Web Vitals is a confirmed ranking signal) and abandonment climbs sharply. The LCP element is usually the hero image, hero text block, or hero video poster.

The fix

**Identify the LCP element first**: DevTools → Performance → record → look for the LCP marker in the timeline.

**Then attack the slowest contributor:**

1. **TTFB heavy** (>800ms) → edge cache the HTML, reduce origin compute. See `page.response.slow`.
2. **Render-blocking CSS** → inline critical CSS, defer the rest.
3. **LCP image** → serve from a CDN, use modern format (AVIF/WebP), preload with `<link rel="preload" as="image" href="hero.jpg">`.
4. **JS-rendered LCP** → switch to SSR or static generation for the hero block.

```html
<!-- Preload the LCP image so it starts downloading before CSS parses -->
<link rel="preload" as="image" href="/hero.avif" fetchpriority="high">
```

References