Alt Text SEO

I treat alt text as a usability optimisation first and an SEO signal second. That ordering protects both. If I prioritise keywords, I end up with text that helps neither a screen reader nor Google's image index. So my rule is: write for a person who cannot see the image, then check whether the keyword fits naturally.

First, I decide the image's role on the page. Is it meaningful (a chart, a product photo, a portrait) or decorative (a spacer, a background pattern, an icon next to a heading)? For meaningful images I write a description. For decorative ones I use alt="". That single decision eliminates most of the bad alt text I see in audits.

When I write the description I keep it under 125 characters. That is not a hard limit from Google—it comes from screen-reader behaviour: JAWS and NVDA cut off longer strings at around that length. For a typical product shot I might write: "Woman in blue down jacket hiking on a snowy ridge." That tells the user the subject, the clothing, and the setting. It also contains the phrase "down jacket" if that is the product's name, but the keyword is secondary to the description.

If the image is a chart or a diagram I write a short summary as the alt text, then I put the full data in a nearby table or paragraph. For example, for a line graph showing organic traffic growth I would write: "Line graph showing organic traffic increasing from 1,200 visits in January to 4,800 visits in June." That is 18 words and under 125 characters. The full monthly breakdown lives in a table beneath the chart. That is the pattern the [W3C advises for complex images](/alt-text/).

One counter-argument I hear is that alt text is purely an accessibility concern and that SEOs should not touch it. I disagree. Google's own guidance for [image search](/image-seo/) says "Use descriptive alt text that helps search engines understand what the image is showing." The two goals overlap. The trick is to write for the person first and let the SEO benefit follow.

The most destructive mistake is leaving meaningful images with no alt attribute or with alt="". That tells screen readers to skip the image entirely, and Google gets nothing but the file name. I see this most often on hero banners and infographics.

Keyword stuffing is the second biggest problem. I have inherited sites where every product image carries alt text like "buy cheap running shoes online running shoes for sale." That is not descriptive; it is spammy. It confuses screen readers and can trigger Google's spam algorithms. If you need to include a keyword, use it once and naturally: "Nike ZoomX Vaporfly running shoes on an asphalt track."

Overdescription is rarer but still an issue. Writing a paragraph for a simple icon wastes the user's time. For a magnifying-glass search icon, alt="Search" is enough. For a logo, the alt text should be the company name, not "blue and white stylised lettering of XYZ Corp."

Context matters. An image of a book on a book-review page should have alt text describing the cover design, not just "book". On a product page, the same image should say "The Great Gatsby paperback cover with a pair of eyes in the sky." The purpose changes the description. [SEO copywriting](/seo-copywriting/) principles apply here: tie the description to the page's intent.

Finally, do not forget to update alt text when you swap an image. I once audited a site where the hero image had been changed from a product shot to a lifestyle photo, but the alt text still said "blue sneakers on a white background." That mismatch hurts both accessibility and trust.

Early in my career I treated alt text as an afterthought. I would write something like "SEO graph" for a chart that showed keyword rankings over six months. That told no one anything. Now I write: "Line graph showing keyword rankings improving from position 15 to position 3 over six months." That is longer but useful.

I also keyword-stuffed product images. On a shoe product page I had the same alt text on every variant: "red Nike running shoes size 10, blue Nike running shoes size 9, green Nike running shoes size 11." I thought I was helping the site rank for "Nike running shoes". In reality I was helping no one. The size is irrelevant to the image; it belongs in the product data. Now I write "Red Nike running shoes on a running track" and let the structured data carry the commerce attributes.

Another thing I got wrong: I used to add alt text to decorative images because I thought every image needed it. I wrote "decorative line separating sections" for a horizontal rule image. That is noise. The correct approach is alt="", which tells the screen reader to ignore the image. I changed that after reading the [W3C's alt decision tree](/alt-text-examples/).

I also undervalued the role of context. For an infographic about SEO steps, I wrote "Infographic showing on-page SEO steps." That describes the form but not the content. Now I would write "Flowchart of six [on-page SEO](/on-page-seo/) steps: keyword research, [title tag](/title-tag/), meta description, headings, content optimisation, [internal links](/internal-links-seo/)." That is longer but gives real value.

The biggest lesson: think of alt text as a signal that the page is well-made, not just a checkbox. When I write good alt text, the page's overall quality rises, and that is what Google rewards in the long run.