Alt text (the alt attribute, sometimes called alt tags or alt descriptions) is a short piece of text attached to an image:
<img src="/images/tankless-install.webp" alt="Plumber installing a tankless water heater on a garage wall" width="1200" height="800">Its first job is accessibility. People who use screen readers hear the alt text in place of the image. If the image fails to load, the browser shows the text instead. Search engines use it as one of the main clues about what an image shows.
Why it matters
Accessibility. Missing alt text leaves blind and low-vision visitors guessing. Accessibility problems also carry legal risk for US businesses under the ADA, and lawsuits over inaccessible websites are common.
Image search. Google Images and Google Lens results bring real traffic in visual industries. For Bean & Barrel Coffee, a product photo with alt text “Bag of Bean & Barrel Ethiopia Yirgacheffe light roast whole bean coffee” gives Google far more to work with than IMG_4471.jpg and an empty alt.
Context for the page. Alt text adds relevant words to the page in a natural way, and when an image is a link, its alt text acts as the link’s anchor text.
Writing good alt text
Describe what the image shows and why it’s there, in plain words, usually in under 125 characters.
| Image | Weak | Better |
|---|---|---|
| Product photo | coffee | 12 oz bag of Colombia Huila medium roast, whole bean |
| Team photo | team | Dr. Patel and two hygienists at Brightside Dental's front desk |
| Before and after | teeth whitening austin best dentist | Patient's smile before and after in-office teeth whitening |
When to leave it empty
Purely decorative images, like background patterns, dividers or an icon next to text that already says the same thing, should have an empty alt attribute: alt="". That tells screen readers to skip them. Leaving out the attribute entirely is different and worse, because some screen readers then read the file name.
Common mistakes
- Stuffing keywords into every alt attribute
- Starting with “Image of” or “Picture of” (screen readers already announce it’s an image)
- Using the same alt text on every product photo
- Putting important text inside images (prices, phone numbers) with no text alternative
How to check
RankThat’s Site Audit lists every image missing alt text. On WordPress, RankThat’s AI fixes can draft alt text for you to review, then the Bridge plugin applies it, with one-click undo. Alt text matters most on product-heavy sites, which is why it’s a staple of ecommerce SEO.