Site speed test

Site speed test

A guide and Core Web Vitals checklist (LCP, CLS, INP) and what affects site speed.

Tools · Performance

Site speed is measured through Core Web Vitals, the three metrics Google uses: LCP (how fast the main element loads), CLS (how stable the layout stays while loading) and INP (how fast the site responds to interactions). This guide shows what affects each metric and what to check for a fast site. Sites on 4shopy are optimized for these values by default.

  • LCP (Largest Contentful Paint): how long the main visual element takes to load. Target: under 2.5 seconds.
  • CLS (Cumulative Layout Shift): layout stability. Target: under 0.1.
  • INP (Interaction to Next Paint): how fast the site answers an interaction. Target: under 200 ms.
  • Driven by: image weight, fonts, third-party scripts and reserved dimensions.

How does it work?

Measure your starting point with a tool such as PageSpeed Insights or Lighthouse — both report LCP, CLS and INP for the page you test.

For a good LCP: optimize and compress images, load the hero image with priority and avoid render-blocking scripts.

For a good CLS: reserve fixed dimensions for images and ads, and load fonts with "display: swap" so text does not jump.

For a good INP: cut the amount of JavaScript executed on interaction and defer non-essential scripts until after the initial load.

Frequently asked questions

What are Core Web Vitals?

Core Web Vitals are three Google experience metrics: LCP (how fast the main content loads), CLS (visual stability) and INP (how fast the site responds to interactions). They are search ranking factors.

How fast should a site load?

The recommended targets are LCP under 2.5 seconds, CLS under 0.1 and INP under 200 milliseconds. Below those values Google considers the experience "good".

What slows a site down most often?

The usual causes are large uncompressed images, too many third-party scripts (chat, analytics, ads), render-blocking fonts, and missing reserved dimensions for images, which cause layout jumps.

How do I test my own site speed?

Use a free tool such as Google PageSpeed Insights or Lighthouse (built into Chrome). You enter the page URL and get the Core Web Vitals scores plus concrete fixes to apply.

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