Are your images slowing the page down?
Images are usually the largest thing on a page and the easiest to fix. Legacy formats, missing srcset and oversized files are the three reasons a page is slow on a phone while it looks fine on your laptop.
Reads the images on a set of pages, checks format and srcset, and measures a few for weight. Saved to your account if you are signed in to a paid plan.
How this check works
Shipwork parses the images on a set of your pages and reports three things: whether any use a modern format (WebP or AVIF), whether they carry a srcset so phones do not download desktop-sized files, and whether the heaviest ones exceed a sensible size. It reads raw HTML and a few image headers, so it sees what a browser actually has to fetch.
What the image weight check measures
The image weight check reads the image tags on the pages it samples, up to 20 in a free run, and looks at their source addresses and attributes. It counts images served from legacy formats such as JPEG, PNG or GIF when none use WebP or AVIF, images with no srcset, and images with no lazy loading.
It then requests a small sample of up to eight image addresses to read the real content type and size from the response, because a server can deliver a modern format from an older-looking address. Images whose response is larger than 250 KB are listed, so the sample reads the served type rather than trusting the file extension.
How to read an image weight result
A legacy-format warning means the images checked used older formats and none served a modern one by type or address. A missing srcset warning means the page offers the browser only one image size, so a phone may download a desktop-sized file. Heavy images over 250 KB are the clearest lead: they are the ones most likely to slow the largest contentful paint.
These are leads, not proof. The tool probes a limited sample, an image request can fail for reasons unrelated to weight, and an image service may transform an image before it reaches a visitor. The check cannot measure real-user speed; it identifies files worth compressing or converting, which you should confirm in a browser.
Common causes and why they matter
Heavy images usually arrive through bulk upload: full-resolution photographs uploaded straight from a camera, theme assets that were never optimised, and banners exported as PNG. Missing srcset is a template issue, because the same single source is printed on every screen size. Missing lazy loading is common on older themes and page builders.
Image weight is often the largest part of a page's total bytes, so it is a direct lever on when the main image appears and how much data a visitor spends. That matters most on mobile connections. Lighter images, responsive sources and deferred below-the-fold loading all improve the first screen without changing the design.
How to fix heavy and slow images
Compress images to a sensible quality and dimensions rather than uploading full-resolution files, then serve WebP or AVIF where the platform supports it. Add srcset so the browser can choose a smaller file on smaller screens, and lazy-load images that sit below the first screen while leaving the main above-the-fold image eager.
On a store, fix this at the source: set your upload and resize rules so new images are compressed on the way in, and check whether an add-on can convert and resize existing ones. Replacing an image means re-uploading it, so correct the process rather than editing a single product. Re-run the check afterwards to confirm the size falls.
When to use related checks
Use image check for alt text and width and height attributes, which is a different question from weight. Use Core Web Vitals when you want what real visitors actually experienced rather than a file-level estimate.
The Core Web Vitals guide and the crawl budget guide cover how image delivery and page weight interact with speed and crawling. Fix the bytes first, then confirm the effect in real-user data.
Questions
Why WebP or AVIF?
What is srcset?
How big should an image be?
How do I check image weight on my website?
Why WebP or AVIF instead of JPEG or PNG?
What is srcset and why does it matter?
Does the image weight check measure my Core Web Vitals?
Keep reading
What this reads
- Reads public pages from outside your network, the way a crawler does.
- No signup, and nothing is stored on the free checks.
- One of 83 checks across discovery, content, markup, trust and catalogue data.
Cool, just ran an audit and got some insights! Let’s see if I can fix them :)
Whoah! this site is crazy, nothing to roast at all
cool as heck, tried it on my blog and the insights it gave are helpful and not bluff.