Image SEO checker

What image SEO covers

Images do three jobs for search. Alt text tells search engines and screen readers what an image shows, which is how images get found in Google Images and how blind visitors know what they're missing. File size and format decide how fast the page loads. And how images sit in the HTML (with dimensions, responsive sizes and sensible loading) decides whether the page jumps around while it loads.

Google's image guidelines ask for the same things this checker looks at: descriptive alt text, images in real HTML image elements rather than CSS backgrounds, and pages that load quickly.

How to read the result

• Missing alt: the image has no alt attribute at all. Add one. If the image is decorative, like a divider or a background flourish, write alt="" so screen readers skip it. An empty alt is correct for decoration, and we don't count it as a problem.
• Alt that looks like a file name (IMG_4032.jpg, hero-banner-final) or runs past about 125 characters. Describe what the image shows in one sentence instead.
• Heavy files: as a rule of thumb, an image over about 200 KB is worth compressing or resizing, and one over 500 KB is likely slowing the page down.
• Old formats: photos saved as JPEG, PNG or GIF are usually much smaller as WebP or AVIF. PNG is still fine for logos, icons and screenshots with sharp edges.
• Missing width and height: without them the browser can't reserve space, so text jumps down when the image arrives.
• No srcset on large images: phones download the full desktop-sized file.

Pixel dimensions are read from the image file itself, so they're accurate even when the HTML says something else. File sizes come from what the server reports, or from the file when it's small enough that we read all of it. When neither is available, the size is left blank rather than guessed.

Lazy loading and the main image

Lazy loading (loading="lazy") tells the browser to wait until an image is about to scroll into view. That's right for images further down the page and wrong for the big image at the top, which is often the largest thing on screen and the one the browser should fetch first. Google's web.dev guidance is to avoid lazy loading images that are visible when the page first opens.

We treat the first large image in the HTML as the likely main image and flag it if it's lazy loaded. That's a guess from the order of the HTML. If your main image is a different one, check that one instead.

Writing alt text that helps

Good alt text says what's in the image, as it relates to the page. "Grey cat asleep on a laptop keyboard" beats "cat", and it beats "cat laptop sleeping cute cat photo" too. Include your keyword only when it honestly describes the image. Stuffed alt text helps nobody and sounds terrible read aloud.

If many images have no alt text, our alt text generator writes a first draft from the image itself. Read it before you publish: it can describe what's in the picture, but it can't know why the picture is on your page.

What this checker can't see

It reads the HTML your server sends. Images added by JavaScript, CSS background images and images inside embedded frames won't appear here. Google doesn't index CSS background images either, so anything that matters should be a real <img>.

It doesn't measure loading speed. For Core Web Vitals and how long your main image really takes to appear, run the page through PageSpeed Insights or our page speed checker.