Your Website Is Slower Than You Think — Find Out Why
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Quick answer
Why is my website slow, and what should I fix first?
A website is almost always slow for one of five reasons, in this order of frequency: oversized images, render-blocking CSS and web fonts, too much JavaScript (usually third-party tags), a slow server response, and layout that shifts while loading. SnapSiteScan runs Google Lighthouse against your page on both mobile and desktop, then ranks your own issues by measured impact so you fix the one that moves the number most — not all forty at once.
- Passing LCP
- Under 2.5 seconds
- Passing INP
- Under 200 milliseconds
- Passing CLS
- Under 0.1
- Good performance score
- 90 or above out of 100
- Measurement source
- Google Lighthouse lab data, mobile and desktop
- Cost and signup
- Free, no account required
What to do next: Run one scan, then fix only the top-ranked recommendation and re-scan. One change typically moves the score 10–20 points.
What counts as a good number, and what each number actually means
These are the thresholds SnapSiteScan grades against. They match Google's published Core Web Vitals limits, so a passing result here is a passing result in Search Console.
| Metric | Good | Needs work | Poor | What it means | Usual cause |
|---|---|---|---|---|---|
| LCPLargest Contentful Paint | Under 2.5 s | 2.5 – 4.0 s | Over 4.0 s | The moment the biggest visible element — usually the hero image or headline — finishes rendering. Visitors read this as “the page has loaded”.Above 2.5 seconds visitors begin noticing the delay. Above 4 seconds many leave before the page finishes loading. | Unoptimised hero image, slow server response, or render-blocking CSS. |
| INPInteraction to Next Paint | Under 200 ms | 200 – 500 ms | Over 500 ms | The delay between a visitor interacting and the screen visibly updating. Above 500 ms the page feels broken rather than slow.Above 200 milliseconds taps feel sluggish. Above 500 milliseconds visitors tap again, believing the page is broken. | Long JavaScript tasks blocking the main thread, often third-party scripts. |
| CLSCumulative Layout Shift | Under 0.1 | 0.1 – 0.25 | Over 0.25 | A unitless score for unexpected movement. It is the metric behind mis-taps and accidental clicks on mobile.Above 0.1 the page visibly moves while being read. Above 0.25 visitors tap the wrong thing, which is how layout shift turns into lost orders. | Images or embeds without reserved width and height, and late-swapping web fonts. |
| TBTTotal Blocking Time | Under 200 ms | 200 – 600 ms | Over 600 ms | The lab stand-in for INP: total time the main thread was busy enough to ignore input. Fix TBT and INP follows.Above 200 milliseconds the page ignores input it appears ready for. Above 600 milliseconds it feels frozen rather than slow. | Large JavaScript bundles, hydration work, tag managers and analytics loading eagerly. |
| FCPFirst Contentful Paint | Under 1.8 s | 1.8 – 3.0 s | Over 3.0 s | The first pixel of real content. A high FCP almost always means the problem is server- or network-side, not front-end code.Above 1.8 seconds visitors are still looking at a blank screen. Above 3 seconds a noticeable share leave before seeing anything at all. | Slow hosting, no caching or CDN, redirect chains, blocking fonts and stylesheets. |
| SISpeed Index | Under 3.4 s | 3.4 – 5.8 s | Over 5.8 s | An average of how complete the page looks over time. It catches pages that show something fast but keep loading for seconds.Above 3.4 seconds the page keeps rearranging itself while being read. Above 5.8 seconds visitors stop waiting for it to settle. | Lazy-loading above-the-fold content, heavy sequential requests, oversized images. |
What your score means, and whether it is worth fixing
| Score | Verdict | What it means for your site | What to do |
|---|---|---|---|
| 90 – 100 | Good | The page is in roughly the fastest quarter of the web. Speed is no longer what limits rankings or conversions here. | Stop optimising speed. Spend the effort on content and conversion instead. |
| 50 – 89 | Needs improvement | Typical for a real business site with a CMS, fonts and a few third-party scripts. Visitors notice the lag on mobile. | Fix the single highest-impact issue — usually images or blocking JavaScript. One change often moves 10–20 points. |
| 0 – 49 | Poor | The page is slower than the large majority of the web. Expect measurable bounce on mobile connections. | Treat it as a structural problem: hosting, image pipeline and script budget, in that order. |
The order to fix things in
Every scan ranks your own issues by measured impact. When you have no scan in front of you, this is the default order — cheapest and highest-impact first.
- 1
Images
Largest share of transferred bytes on most sites and the usual LCP element. Cheapest win per hour spent.
- 2
Render-blocking CSS and fonts
Delays every paint on the page, so it degrades FCP and LCP at the same time.
- 3
JavaScript and third-party scripts
Dominates TBT and INP. Removing one unused tag often beats weeks of code tuning.
- 4
Server response and caching
Sets the floor no front-end fix can get under.
- 5
Layout stability
Cheap to fix with explicit dimensions, and it directly reduces mis-taps on mobile.
Website Speed & Core Web Vitals Guides
Learn how to test, measure, and improve your site's performance
Why Is My Website Slow?
The most common reasons websites load slowly — and how a scanner helps you spot them in seconds.
How to Fix a Slow Website
Step-by-step fixes for the most common causes of poor page speed, written for non-developers.
Core Web Vitals Explained
LCP, INP, and CLS — what they mean, why Google cares, and how to improve each one.
The Complete Guide to INP
Everything you need to know about the Core Web Vital that replaced FID — and how to fix it.
What Is a Good PageSpeed Score?
What counts as a good score, how it's calculated, and realistic targets for mobile and desktop.
Choosing a Website Speed Test Tool
A practical comparison of the most popular speed test tools — and which metrics actually matter.
More performance guides
- The Complete Website Audit Guide: Speed, SEO, and UX Explained
- What Google PageSpeed Insights Really Does — And Why It Matters for Your Website
- Why Website Speed Matters More Than Ever — And How It Shapes User Behavior
- How to Make Your Website Faster in 2025
- How Accurate Are Website Speed Tests in 2025? What You Need to Know
- Mobile vs Desktop Performance: Why Testing Both Matters in 2026
- Website Performance Budgets: How to Set and Maintain Them in 2026
- Server Response Time: The Hidden SEO Factor Most Sites Ignore
- How to Run a Website Audit (Step-by-Step Guide for 2026)
Related SEO reading
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