Core Web Vitals
Core Web Vitals (CWVs) are Google’s standardised metrics for measuring real-world user experience. PerfLeaf measures all five key metrics using a real headless browser.
Metrics
Section titled “Metrics”LCP — Largest Contentful Paint
Section titled “LCP — Largest Contentful Paint”Time until the largest visible content element (image, video, or text block) is rendered.
| Rating | Threshold |
|---|---|
| Good | ≤ 2.5 s |
| Needs improvement | 2.5 – 4.0 s |
| Poor | > 4.0 s |
CLS — Cumulative Layout Shift
Section titled “CLS — Cumulative Layout Shift”Total unexpected layout shift score during page load. Lower is better.
| Rating | Threshold |
|---|---|
| Good | ≤ 0.1 |
| Needs improvement | 0.1 – 0.25 |
| Poor | > 0.25 |
INP — Interaction to Next Paint
Section titled “INP — Interaction to Next Paint”Measures responsiveness to user interactions. Replaces FID as of March 2024.
| Rating | Threshold |
|---|---|
| Good | ≤ 200 ms |
| Needs improvement | 200 – 500 ms |
| Poor | > 500 ms |
FCP — First Contentful Paint
Section titled “FCP — First Contentful Paint”Time until the browser renders the first piece of DOM content (text, image, SVG).
| Rating | Threshold |
|---|---|
| Good | ≤ 1.8 s |
| Needs improvement | 1.8 – 3.0 s |
| Poor | > 3.0 s |
TTFB — Time to First Byte
Section titled “TTFB — Time to First Byte”Time from the request being sent until the first byte of the response is received. Reflects server response speed.
| Rating | Threshold |
|---|---|
| Good | ≤ 800 ms |
| Needs improvement | 800 ms – 1.8 s |
| Poor | > 1.8 s |
In the report
Section titled “In the report”The Core Web Vitals card shows average values across all crawled pages with colour-coded pass/fail indicators. Click any individual page in the Pages Analysed list to see page-specific CWV values.
Common fixes
Section titled “Common fixes”| Issue | Fix |
|---|---|
| High LCP | Optimise images, preload hero assets, reduce render-blocking resources |
| High CLS | Set explicit width/height on images and embeds, avoid injecting content above the fold |
| High INP | Reduce long tasks, defer non-critical JS, optimise event handlers |
| High FCP | Reduce server response time, eliminate render-blocking CSS/JS |
| High TTFB | Use CDN, optimise server-side rendering, enable caching |