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Website Performance

Website Speed Checker: Is Your Site Losing You Customers?

Run a website speed test, understand why a site is slow, and use Core Web Vitals to prioritise practical improvements for real users.

· 7 min read · Intellivise Insights

A slow website is not one metric or one score. It can be a server response issue, a large hero image, too much JavaScript, unstable layout, or a mobile experience that breaks under real network conditions. Start with PageSpeed Insights, then use the evidence to isolate the right work.

Key takeaways

  • PageSpeed Insights combines real-user field data with Lighthouse lab diagnostics; use both for different questions.
  • Core Web Vitals target loading (LCP), responsiveness (INP), and visual stability (CLS).
  • Fix the bottleneck shown by the data, then retest the same priority URLs instead of chasing a single cosmetic score.

How to run a website speed test

Open PageSpeed Insights, enter one representative URL, and inspect mobile and desktop results. Where available, field data represents a 28-day view of real Chrome user experience; lab data gives a controlled place to debug.

Test a homepage, a commercial landing page, a product or service page, and the main conversion path. Record the URL, date, device view, and metrics so the next comparison is meaningful.

  • Start with the pages that matter commercially.
  • Compare field and lab data rather than treating them as a contradiction.
  • Retest after focused changes.

Why a website can be slow

Slow LCP often points toward server response, redirects, render-blocking resources, or a large above-the-fold asset. Poor INP can reveal heavy JavaScript and long tasks. High CLS can come from missing image dimensions, late-inserted content, fonts, ads, or personalisation.

These are investigation prompts, not automatic diagnoses. Use browser tooling and a controlled test to confirm the cause before changing the build.

  • LCP: loading and largest visible content.
  • INP: delay after a real interaction.
  • CLS: movement after a page appears ready.

Core Web Vitals in plain language

Google’s good thresholds are LCP at 2.5 seconds or less, INP below 200 milliseconds, and CLS below 0.1. These are user-experience signals, not a single pass/fail business or ranking score.

Use the scorecard above to organise supplied values, then return to PageSpeed Insights and Search Console for the detailed evidence that explains what to fix.

  • Prioritise the metric furthest outside the good threshold.
  • Keep image dimensions and critical assets intentional.
  • Reduce unnecessary third-party and JavaScript work.

Turn a diagnosis into an improvement plan

Confirm a field problem first when field data exists, reproduce it in a controlled environment, group fixes by bottleneck, ship the smallest focused change, and monitor the same page group for regressions.

Measure commercial outcomes separately. Faster pages can improve usability, but an audit should not promise a fixed traffic, ranking, or revenue result.

  • Server and critical-resource work.
  • Image, font, and layout-stability work.
  • JavaScript and third-party-script work.

Sources

  1. Google Search Central: Core Web Vitals and Search
  2. web.dev: Core Web Vitals workflows with Google tools
  3. web.dev: Why lab and field data can differ
  4. PageSpeed Insights

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