Why alt text matters
Alt text is the description of an image for anyone who cannot see it: screen reader users, people on slow connections, and search engines. Google Images relies on it to understand what a picture shows, and it is one of the few signals an image carries into search. Missing alt text is also one of the most common accessibility failures on the web.
Missing, empty and present
The checker sorts images into three groups, and they are not equally bad.
- Missing. No
altattribute at all. Screen readers often read out the file name instead, which is noise. Every image needs the attribute. - Empty (`alt=""`). Correct for purely decorative images such as dividers, background flourishes and icons next to text that already says the same thing. It tells assistive technology to skip the image.
- Present. Has a description. The checker also flags weak ones: alt text that is a file name, a generic word like "image" or "logo", or longer than about 125 characters.
Writing good alt text
- Describe what the image shows and why it is there, in one short sentence.
- For a product screenshot, say what the screen shows: "Dashboard with weekly revenue chart and three KPI cards".
- For a logo that links home, use the company name, not "logo".
- For charts, give the takeaway, and put the full data in the text nearby.
- Do not start with "image of". Screen readers already announce it as an image.
- Do not stuff keywords. Write for the person who cannot see it.
Images this tool cannot see
It reads <img> tags in the HTML, including common lazy-load attributes like data-src. CSS background images and images inserted by JavaScript are not listed. Background images cannot carry alt text, so anything meaningful should be an <img>. For the rest of the page, run the SEO checker.