If you’ve already read our overview on whether alt tags matter for SEO, you know the short version: yes, but only when it’s written well. This post is the practical follow-up — the actual rules, examples, and edge cases for writing alt text that works for screen readers, search engines, and the humans reading your content all at once.
Quick definition if you’re landing here directly: alt text is the written description added to an image’s HTML alt attribute, read aloud by screen readers and used by search engines to understand what an image shows.
The core rules
Be specific, not generic. “Shoe” tells a screen reader user almost nothing. “Men’s blue running shoe with white sole, side angle” tells them exactly what they’re looking at.
Keep it to roughly 100–125 characters. Most screen readers don’t cut off alt text, but long descriptions become tedious to listen to, and search engines give diminishing returns past this point anyway. If you’re written a full paragraph, you’re writing a caption, not alt text.
Include a keyword only if it fits naturally. If your target keyword is “ceramic mug,” and the image genuinely is a ceramic mug, use it. If you’re bending the description to force a keyword in, stop — it reads as spam to both users and crawlers.
Skip “image of” or “picture of.” Screen readers already announce that an image is present before reading the alt text. Saying it again is redundant noise that makes every single description longer for no reason.
End with a period. Minor detail, but it gives screen readers a natural pause before moving to the next element on the page.
A decision framework: not every image needs the same treatment
This is the part most guides skip, and it’s the difference between alt text that helps and alt text that’s just there for SEO’s sake.
Informative images (product photos, blog illustrations, team headshots) — describe what’s shown and why it’s relevant to the surrounding content.
- Good:
alt="Sourdough loaf cooling on a wire rack, crust split open"
Decorative images (background textures, dividers, purely aesthetic flourishes) — use an empty attribute, alt="". This tells screen readers to skip the image entirely rather than wasting the user’s time on something with no informational value.
- Good:
alt=""(not omitted entirely — an empty value is intentional and correct)
Functional images (icons used as buttons, images that act as links) — describe the action or destination, not the visual.
- Bad:
alt="magnifying glass icon" - Good:
alt="Search"
Images containing text (banners, infographics, screenshots with on-image labels) — include the actual text shown, since it’s otherwise invisible to screen readers and crawlers.
- Good:
alt="Banner reading: Free shipping on orders over $50"
Complex images (charts, diagrams, data visualizations) — a single alt attribute usually can’t capture everything. Write a brief alt description and follow it with a fuller text explanation in the surrounding content or a linked long description.
Good vs. bad, side by side
| Image | Bad alt text | Good alt text |
|---|---|---|
| Product photo | alt="product1.jpg" |
alt="Navy wool peacoat, front view, brass buttons" |
| Recipe hero shot | alt="food" |
alt="Bowl of chocolate avocado mousse topped with raspberries" |
| Decorative divider | (missing entirely) | alt="" |
| Linked logo | alt="logo" |
alt="Acme Co. homepage" |
| Infographic | alt="infographic" |
alt="Infographic: 5 steps to onboard a new employee, listed below" |
Where SEO and accessibility pull in different directions
Most of the time, writing for accessibility and writing for SEO point the same direction — a clear, specific description serves both. But there’s a genuine tension worth naming: accessibility best practice says to avoid restating “image of,” while some SEO advice pushes toward keyword-dense descriptions that can tip into being unnatural for a screen reader to sit through. Google’s own staff have spoken to this balance directly — it’s worth a read if you want the source rather than secondhand advice. (Search Engine Journal covered the discussion here.)
The resolution is simple in practice: write for the human listening first. If a keyword fits naturally into an accurate description, include it. If it doesn’t, leave it out. Accessibility wins the tiebreak every time — and as it happens, that’s usually what performs better in image search anyway.
Alt text is one piece of a bigger picture
Alt text is the highest-leverage single thing you can do for image SEO, but it isn’t the only one — file naming, compression, and image format all play a supporting role too. If you want the fuller picture beyond alt text specifically, Search Engine Journal’s image SEO tips covers the adjacent practices worth knowing. And if you’re dealing with a large existing catalog rather than writing fresh, that’s a different problem — see our audit guide for how to find and fix issues at scale.
What happens when you skip these rules
Most of the mistakes that undercut alt text’s SEO value — keyword stuffing, duplicate descriptions across near-identical images, alt text that no longer matches the image after a swap — are direct violations of the rules above. We’ve broken each one down individually, with what to do instead, in 7 alt text mistakes that are quietly hurting your SEO.
The takeaway
Good alt text isn’t complicated, but it does take a moment of actual thought per image rather than a copy-pasted template. Describe what’s there, keep it tight, skip the filler phrases, and let keywords show up only when they belong. Do that consistently and the SEO benefit takes care of itself.
This post is part of a series on image SEO. Start with the overview: Are Alt Tags Important for SEO? Or continue to: 7 Alt Text Mistakes Hurting Your SEO · Alt Text vs. Title vs. Caption · How to Audit and Fix Alt Text