GTmetrix Performance Blog

News, updates and guides on GTmetrix and general web performance

Lighthouse 8.3.0 Update

We’ve upgraded GTmetrix to Lighthouse 8.3.0 – read on for changes that come with this release.


Lighthouse 8.3.0

Moving from Lighthouse 7.4.0 to 8.3.0 saw a few notable changes, primarily the re-weighting of Performance scores.

Performance Score Re-weighted

The Performance score is compromised of 6 individual metrics that were weighted and combined to produce a single score.

With our update to Lighthouse 8.3.0, these individual metrics have been adjusted with a new weighting:

  • First Contentful Paint (FCP)
    • Previously 15%, now at 10% (▼ 5%)
  • Speed Index (SI)
    • Previously 15%, now at 10% (▼ 5%)
  • Time to Interactive (TTI)
    • Previously 15%, now at 10% (▼ 5%)
  • Total Blocking Time (TBT)
    • Previously 25%, now at 30% (▲ 5%)
  • Cumulative Layout Shift (CLS)
    • Previously 5%, now at 15% (▲ 10%)
  • Largest Contentful Paint (LCP)
    • No Change – Remains at 25%

This new weighting places more importance on reduced JavaScript execution and a more visually stable page load.

For more specifics on the weighting change, read Lighthouse’s official FAQ.


Other Relevant Changes from Lighthouse 7.4.0 to 8.3.0

  • Properly size images audit will now ignore images larger than the viewport
  • “Serve images in next-gen formats” audit key (serve-images-in-next-gen-formats) is renamed to “modern-image-formats”
    • Applicable to API users only
  • Serve images in next-gen formats now includes AVIF estimates
  • Temporarily disable all preload audits
    • Including “Preload key requests” and “Preload Largest Contentful Paint image”
    • Preloading is still a good strategy to practice, however aggressive preloading can cause performance issues (i.e. preloading everything)
    • Further discussion/research is needed on how to better present preloading recommendations in the audits (Source)
  • Fixed resource size calculation of cached images



More GTmetrix Fixes

We’ve also tweaked and fixed a few other Lighthouse related issues:

  • Fixes to Speed Visualization (Filmstrip)
    • Corrected situation where the Speed Visualization extended past the Fully Loaded time in some conditions
  • Fixes to Lighthouse and Redirected Pages
    • Fixed Lighthouse abort errors with certain odd redirects
    • Fixed missing items in critical request changes with certain redirect conditions



General updates and improvements

More changes in this release:

Analysis Option Flags on Dashboard Now Show Regions Within Countries

To help differentiate locations within the same country, we’ve added abbreviations to flag icons.

Flags now show specific location abbreviations to better discern test locations within the same country.

You can now see at a glance which specific location within a country you’ve tested in.


Other Updates

  • PDF Report Fixes
    • Fixed PDF styling bug where content overlapped the header in Full Reports in some cases
  • API Documentation Updates


Let us know if you run across any bugs or issues and feel free to tell us your thoughts on Twitter (@gtmetrix) or contact us.


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