How to use the Image Alt Checker
- Enter the page URL and click Check images.
- Read the summary: images missing alt text, oversized files, missing dimensions and broken URLs.
- Use the filters to show only the problem images, then fix them in your CMS or code.
- Click Export CSV to hand the list to your content or development team.
What is an image alt checker?
An image alt checker scans a web page for <img> elements and reports the alt attribute of each one, together with technical details that affect SEO and performance. Alt text (alternative text) is read aloud by screen readers, shown when an image fails to load, and used by search engines to understand what an image shows — which matters for Google Images and for the relevance of the page itself.
Missing alt vs. empty alt
These two cases look similar but mean very different things:
| Markup | Meaning | Verdict |
|---|---|---|
<img src="team.jpg"> | No alt attribute. Screen readers may announce the file name instead. | Error — always add an alt attribute. |
<img src="divider.svg" alt=""> | Empty alt: the image is decorative and screen readers skip it. | Correct for purely decorative images. |
<img src="team.jpg" alt="Our five-person support team in the Berlin office"> | Descriptive alt text. | Correct for informative images. |
This follows WCAG success criterion 1.1.1 (Non-text Content). Good alt text describes the image's purpose in context, is concise — about 125 characters is a common guideline — and does not start with “image of”. Don't stuff keywords into it; describe what is shown, and the relevant words usually appear naturally.
Performance checks
- File size: we send a HEAD request for up to 40 images and read their
Content-Length. Images over 200 KB are flagged; they slow down Largest Contentful Paint, especially on mobile. Compress them with the Image Compressor or resize them with the Image Resizer. - Width and height attributes: without them the browser can't reserve space before the image loads, so content jumps — measured as Cumulative Layout Shift (CLS), a Core Web Vital.
- Modern formats: WebP and AVIF are typically much smaller than JPEG or PNG at similar quality; SVG is ideal for logos and icons.
- Lazy loading:
loading="lazy"defers off-screen images. Don't lazy-load the hero image at the top of the page — it delays LCP. - Broken images: URLs answering with 4xx/5xx waste crawl budget and show a broken icon to users.
The checker reads <img> tags in the server-rendered HTML; CSS background images and images inserted by JavaScript are not included. For the full on-page picture, run the SEO Checker.
Tools that pair well with the Image Alt Checker
- Heading Checker — Visualise the heading outline of any page.
- Meta Tag Checker — See exactly how Google is likely to display your page: title and description measured in pixels, desktop and mobile previews, and every meta tag in the <head>.
- Keyword Density Checker — Enter a URL and the keyword it should rank for.
- Open Graph Checker — Preview how your link will look when shared on Facebook, LinkedIn, X and Slack.
Frequently asked questions
Do all images need alt text?
alt attribute. Informative images need descriptive text; purely decorative images (spacers, background flourishes) should use an empty alt="" so screen readers skip them.Does alt text help SEO?
Why is the file size shown for only some images?
What is the ideal image file size?
Is the title attribute a replacement for alt?
title attribute shows a tooltip on hover and is not reliably read by screen readers. Always use alt.