How this speed test works
The test runs Google's Lighthouse engine through the PageSpeed Insights API on a simulated mid-range phone with a throttled connection. That is deliberately harsher than your own laptop on office Wi-Fi, because it is closer to what many of your visitors experience and to what Google measures.
It also times how long your server takes to respond from our side and reads the page for common problems such as uncompressed HTML and missing caching headers. The test can take up to 30 seconds.
Core Web Vitals explained
Google uses three Core Web Vitals as part of its page experience signals. The "good" thresholds are:
- Largest Contentful Paint (LCP): under 2.5 seconds. How long until the main image or text block appears.
- Interaction to Next Paint (INP): under 200 milliseconds. How quickly the page responds to taps and clicks. INP replaced First Input Delay in March 2024. Lab tests like this one use Total Blocking Time as the closest stand-in.
- Cumulative Layout Shift (CLS): under 0.1. How much the page jumps around while loading.
The usual culprits
- Huge images. Resize to the size they are displayed at and serve WebP or AVIF.
- Too much JavaScript, especially third-party chat, tracking and advert scripts.
- Render-blocking CSS and fonts in the <head>.
- Slow hosting or no page caching, which shows up as a long server response time.
- Images and embeds without width and height, which cause layout shift.
Further reading: How to Improve Your Core Web Vitals in 2026