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Performance Scanner

Core Web Vitals,
graded and explained.

Real field vitals need a browser, but most performance problems are visible in the response. This scan estimates LCP, CLS, and INP risk from TTFB, render-blocking resources, image hygiene, compression, caching, and protocol — and grades it Lighthouse-style with the exact fixes that move each metric. A lab heuristic, honestly labelled.

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3
Web Vitals
9
Lab signals
A–F
Grade scale
p75
Google target

The three vitals

What Google measures, and what drives it

LCP≤ 2.5s

Largest Contentful Paint

Driven by: TTFB, render-blocking resources, hero image weight

CLS≤ 0.1

Cumulative Layout Shift

Driven by: images without width/height, injected content, web fonts

INP≤ 200ms

Interaction to Next Paint

Driven by: JavaScript execution, third-party scripts, long tasks

What gets checked

Nine lab signals, three categories

Core Web Vitals (lab)

  • LCP risk from TTFB + render path
  • CLS risk from image dimension hygiene
  • INP risk from script + third-party weight
  • Lighthouse-style A–F grade
  • Per-vital risk: low / medium / high

Load Path

  • Server response time (TTFB)
  • Render-blocking head scripts (sync, no async/defer)
  • Blocking stylesheets
  • Transport protocol: HTTP/2 vs HTTP/3
  • Document size

Delivery Hygiene

  • Brotli / gzip compression
  • Cache-Control (max-age, immutable)
  • Image lazy-loading coverage
  • Modern image formats (WebP / AVIF)
  • Third-party domain count

Live scanner

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