Alt Attribute SEO
The alt attribute is HTML text added to an image that describes what the image shows or does, so search engines and screen readers can understand it when the image is unavailable.
Start here
- Add alt text to every meaningful image — it's free SEO and accessibility value
- Write naturally: describe what the image shows, don't stuff keywords
- Use empty alt text for decorative images so screen readers skip them
- Keep it under 125 characters and test with a screen reader
- Don't confuse alt text with the title attribute — they serve different purposes
What I'd do first
- Add alt text to every meaningful image on your site — don't skip any
- Keep descriptions under 125 characters and describe what the image actually shows
- Include your target keyword naturally if it fits the description, but never force it
- Use empty alt text (
alt="") for decorative images like borders or spacers - Test with a screen reader (like VoiceOver on Mac) to hear how your alt text sounds
Plain-English take
The alt attribute is a little piece of HTML you add to an image tag. It's the text that shows up when an image fails to load, and it's what screen readers speak aloud for people who can't see the image. For search engines, it's a clue about what the image contains — because Google's image recognition still isn't perfect. Think of it as a caption for machines and a lifeline for accessibility.
When it actually matters
- Image-heavy pages like product galleries, infographics, or photo portfolios — alt text is your only way to tell search engines what those images mean
- E-commerce product images — good alt text can help products show up in Google Image Search, which drives traffic
- Accessibility compliance — if your site serves a broad audience (or you're in a regulated industry), missing alt text is a legal risk
- Decorative images — this is where people get it wrong: you should use empty alt text, not skip the attribute entirely
What I got wrong
- I used to stuff keywords into alt text thinking it would boost rankings. It doesn't — it just makes the experience worse for screen reader users and can look spammy to Google
- I left alt text blank on important images because I was in a hurry. That's a double loss: no accessibility and no SEO value
- I wrote things like "image of a" or "photo showing" — that's wasted characters. Just describe the content directly
- I confused alt text with captions. Captions are visible to everyone; alt text is a behind-the-scenes description
Next step
Quick answers
What is alt text in SEO?
Alt text (alternative text) is an HTML attribute added to an image tag that describes the image content. It helps search engines understand images and improves accessibility for screen reader users.
Does alt text help SEO?
Yes, alt text helps search engines interpret image content, which can improve image search rankings and page relevance. However, it is not a direct ranking guarantee.
How do I write good alt text?
Write concise, descriptive text that accurately describes the image content or function. Include relevant keywords naturally, avoid keyword stuffing, and keep it under 125 characters.
What is the difference between alt text and title attribute?
Alt text provides a textual alternative for images when they cannot be displayed, while the title attribute offers additional information as a tooltip. Alt text is essential for accessibility; title is optional.
Sources
Primary documentation is linked directly. Anything commercial is marked nofollow.
- Google Search Central — Best source for Google's guidance on image SEO and how Google interprets image text.
- W3C WAI — Authoritative accessibility guidance on alternative text and non-text content.
- MDN Web Docs — Clear technical reference for the HTML `alt` attribute and proper usage.
Notes from Callum Bennett.