Key takeaways
- Alt text describes what an image shows, for screen readers and for Google.
- Google calls it the most important attribute for giving it information about an image.
- Describe the image in context, in a short sentence. Do not list keywords.
- Decorative images get an empty alt, so screen readers skip them.
What is alt text?
Alt text, or the alt attribute, is a short written description added to an image in the page code. Screen readers read it aloud to people who cannot see the image, browsers show it when the image fails to load, and search engines use it, together with the page text, to understand what the image shows.
In code it looks like this: <img src="red-trail-shoe.jpg" alt="Red trail running shoe with a thick rubber sole">. Google's image SEO best practices call alt text the most important attribute for giving it extra information about an image. It also helps the people using your site with a screen reader, which is why it is a basic accessibility requirement and not just an SEO trick.
How do I write good alt text?
Describe what the image shows and why it is on the page, in one short sentence a person could read aloud. Be specific: color, model, material or action. Use the product name if it is visible. Do not start with image of, do not repeat the caption and never list keyword variations, which Google warns can be treated as spam.
Google uses a simple example: a missing alt is bad, a list of puppy-related keywords is bad, and "Dalmatian puppy playing fetch" is best. Here is the same idea applied to a store:
| Version | Alt text | Verdict |
|---|---|---|
| Missing | (none) | Google and screen readers get nothing |
| Stuffed | lawn mower blade, mower blades, best mower blade cheap, buy blade | Unreadable and risky |
| Generic | product image | Says nothing useful |
| Good | 21-inch replacement lawn mower blade with mounting holes | Clear, specific, honest |
I supervise SEO for 18 US online stores that sell outdoor power equipment parts, with more than 3 million products between them. For parts, the useful detail is what a buyer checks before ordering: size, shape and how it mounts. That detail belongs in the product title and description first, and the alt text follows it. On catalogs this size we write rules per category, so alt text is generated from real product data instead of being typed by hand.
Does every image need alt text?
No. Images that only decorate the page, like background shapes, dividers or a photo that repeats the text next to it, should have an empty alt attribute, written as alt with two quotes and nothing inside. Screen readers then skip them. Images that carry information, or that work as links or buttons, always need a real description.
The W3C's alt decision tree is the clearest guide I know for this. In short:
- Informative image (a product photo, a team photo, a before-and-after): describe what it shows.
- Functional image (a logo that links home, a cart icon): describe the action or destination, for example "Home" or "View cart".
- Image of text: write the text itself in the alt.
- Chart or infographic: give a short alt and put the full data in the page text.
- Decorative image: empty alt.
Alt text for online stores, step by step
- Start with the main product photo. It is the one that shows in Google Images and in shopping results.
- Use the data you already have. Product name, color, size and material from the catalog make a solid alt.
- Give each angle its own alt. "Back view showing the zipper pocket" is more useful than repeating the title five times.
- Name files clearly. Google recommends short, descriptive file names, such as red-trail-shoe.jpg instead of IMG00023.jpg.
- Translate alt text on multilingual sites. The Spanish page needs Spanish alt text and, ideally, Spanish file names.
Alt text is one piece of the product page. Google's e-commerce best practices and Product structured data cover the rest of what makes a product easy to understand. Together they are the core of e-commerce SEO, and if you sell on Shopify, my Shopify SEO checklist shows where to edit alt text in the admin.
How do I find images without alt text?
Run a crawl with a tool such as Screaming Frog, which lists every image with missing or very long alt text, or check single pages with the accessibility audit built into Chrome's Lighthouse. Start with templates: on most sites, fixing the product or blog template corrects thousands of images at once, instead of editing them one by one.
Missing alt text is one of the most common findings in the audits I run, together with oversized images that slow pages down. Both are fixed at the template level when the site is built well, which is why I review them in every website I design or rebuild. To see where your site stands, book the free 30-minute diagnosis from the home page.
Frequently asked questions
How long should alt text be?
Usually one short sentence. Say what matters in the image and stop there: a long alt is tiring to listen to and adds nothing for Google.
Should I put keywords in alt text?
Only if they describe the image honestly. A product name in the alt of that product's photo is fine. A list of search terms is not.
Is alt text the same as the image title?
No. The title attribute shows as a tooltip on hover and is optional. The alt attribute is what screen readers and Google rely on.
Does alt text help in AI search?
It helps search systems understand images on your page. The bigger factor is still clear, useful text on the page itself.
Can AI write my alt text?
It can draft it, but review it. Automatic descriptions miss what matters to a buyer, like the exact model or size.
About the author
Juan José Giraldo is an SEO consultant in Medellín, Colombia, with 5+ years of experience. He works on technical and local SEO for 600+ US car dealerships at Reunion Marketing, an Inc. 5000 agency, and supervises the SEO of 18 US online stores with more than 3 million products at Prontomowers. Read more · LinkedIn.