Responsive images

Silktide loads your pages in a real browser and compares each image's actual dimensions against the size it is displayed at. Images that are much larger than they appear on screen are reported, along with the data wasted by the extra resolution.

Why this matters

A common pattern: a 4000-pixel photo is uploaded, and the page displays it 400 pixels wide. Visitors download the full-resolution file - potentially megabytes

to see what a far smaller file would render identically. The waste is worst on phones, which have the smallest screens and often the slowest, most expensive connections. Faster pages keep more visitors and feed into search ranking through .

How to fix it

Provide each image in several sizes and let the browser pick the right one for the device:

<!-- The browser downloads only the size it needs -->
<img src="flower-800.jpg"
     srcset="flower-400.jpg 400w, flower-800.jpg 800w, flower-1600.jpg 1600w"
     sizes="(max-width: 600px) 100vw, 50vw"
     alt="Flower stall at the market">

Automate the resizing. Most generate multiple sizes on upload, and can resize on delivery - either stops the problem recurring.
As a minimum, resize one-off images to roughly the size they are displayed before uploading them.

How Silktide tests this

Load the page in a real browser and record the size each image is displayed at, accounting for the sharper screens on modern devices.
Compare that with the dimensions of the image file actually downloaded.
Report images where the excess is meaningful, with the bytes that a right-sized image would save, largest first.

Troubleshooting

How does this differ from the other image checks?

This check is about dimensions: serving a physically larger image than the page displays. Image compression and Image optimisation cover making the file smaller at the same dimensions, and Modern image formats covers converting to WebP or AVIF. The same image can appear in several - the fixes are complementary.

The image looks sharp because of high-resolution screens

Modern screens do need more pixels than the displayed size suggests, and the measurement allows for that. Images are only reported when they exceed what even a high-resolution screen can use.