Check 11 / 12 LOW impact In the full checklist
Compress hero images to WebP under 150kb
What this check is
The hero image is usually the largest contentful paint element, so its file size decides the mobile score more than any other asset.
How to implement it
Export the hero at the dimensions it actually renders at each breakpoint, compress it to WebP or AVIF under a small budget, and serve the phone-sized version to phones rather than scaling down the desktop file. Keep the aspect ratio to avoid layout shift.
How to verify it
Confirm the hero response is under the size budget in a modern format, and that the image element declares width and height so no space is reserved twice.
All 197 checks, one Google Sheet
This page is the summary. The full checklist carries the priority, the impact score and the tool link for every check — all 197 of them, across 14 categories, as a Google Sheet and CSV with lifetime updates.
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