Performance Scan and Core Web Vitals
The performance scan measures Core Web Vitals — the speed and stability signals Google uses as ranking factors. Here is what each metric means and how to improve them.
Performance Scan and Core Web Vitals
Google uses Core Web Vitals as direct ranking signals. A slow or visually unstable website ranks lower in search results, regardless of content quality. The performance scan measures these metrics from the perspective of a real browser loading your page.
Credit Cost
A performance scan costs 3 credits and runs as part of a Full SEO Scan (1,500 credits) or can be triggered as a standalone check.
The Core Web Vitals
LCP — Largest Contentful Paint
What it is: The time from when the page starts loading to when the largest visible content element (image, video, or large text block) is fully rendered.
Why it matters: LCP measures perceived load speed. A slow LCP makes the page feel broken.
| LCP | Rating |
|---|---|
| Under 2.5s | Good |
| 2.5s - 4.0s | Needs improvement |
| Over 4.0s | Poor |
Common causes of poor LCP:
- Large unoptimized images
- Render-blocking JavaScript
- Slow server response (high TTFB)
- No CDN for static assets
CLS — Cumulative Layout Shift
What it is: How much the visible content shifts unexpectedly while the page loads. Measured as a score from 0 (no shift) upward.
Why it matters: CLS captures visual instability. If buttons move while you are about to click them, that is a high CLS.
| CLS | Rating |
|---|---|
| Under 0.1 | Good |
| 0.1 - 0.25 | Needs improvement |
| Over 0.25 | Poor |
Common causes of poor CLS:
- Images without declared width/height dimensions
- Late-loading ads that push content down
- Web fonts causing text to reflow
FCP — First Contentful Paint
What it is: The time until the first piece of content (text, image, SVG) is rendered to the screen.
Why it matters: Users need visual feedback that the page is loading. A delayed FCP makes the page feel broken.
| FCP | Rating |
|---|---|
| Under 1.8s | Good |
| 1.8s - 3.0s | Needs improvement |
| Over 3.0s | Poor |
TTFB — Time to First Byte
What it is: Time from the request being sent to the first byte of response being received. Pure server speed.
Why it matters: TTFB is the foundation of all other metrics. A high TTFB means everything else is slower too.
| TTFB | Rating |
|---|---|
| Under 600ms | Good |
| 600ms - 1.5s | Needs improvement |
| Over 1.5s | Poor |
What the Performance Report Shows
The performance scan report includes:
- LCP, CLS, FCP, TTFB measurements with ratings
- Page weight (total bytes transferred)
- Number of requests
- Render-blocking resources identified
- Oversized images flagged
- Recommendations for improvement
Common Fixes
| Issue | Fix |
|---|---|
| High LCP | Compress images, use WebP format, add CDN |
| High CLS | Add width/height to all images and iframes |
| High FCP | Reduce render-blocking JS, inline critical CSS |
| High TTFB | Upgrade server, add caching, use a CDN |
| High page weight | Enable gzip/brotli compression, minify CSS/JS |