Alt Text SEO
Alt text is the HTML text alternative for an image, used to describe the image's content or function when the image cannot be seen.
What I’d do first
- Audit your images for missing or generic alt text.
- Write descriptive, concise alt text under 125 characters.
- Use keywords naturally — never stuff.
- Use empty alt text for decorative images.
- Test with a screen reader to catch issues.
I used to think alt text was just a checkbox for accessibility. I was wrong.
The path I'd take
- Identify the image's purpose. Is it informative, decorative, or functional (like a button)? That decides whether you write a description or use
alt="". - Describe the content, not the file. Don't say "image of a red car". Say "Red sedan parked in front of a mountain range at sunset."
- Keep it under 125 characters. Screen readers cut off longer text. If you need more, use a short alt text and a longer description nearby.
- Use keywords naturally. If the image is a "blue ceramic coffee mug", and your page is about coffee mugs, that's fine. Don't force "best blue ceramic coffee mug for sale".
- Skip fluff. No "image of" or "picture of". Screen readers announce it's an image. Just describe.
- Test with a screen reader. Use VoiceOver (Mac) or NVDA (Windows) to hear how your alt text sounds. It's the best way to catch awkward phrasing.
Watch-outs
- Blank alt text on meaningful images. This is the biggest sin. If you leave it empty, screen readers skip the image entirely, and search engines get nothing.
- Keyword stuffing. I've seen alt text like "buy cheap running shoes online running shoes for sale". That hurts usability and can get you flagged.
- Repeating the caption. If the caption already says "Figure 1: Revenue by quarter", don't copy that into alt text. Describe what the chart shows, like "Bar chart showing revenue increasing from Q1 to Q4."
- Forgetting decorative images. Use
alt=""for spacer images, background patterns, or purely decorative elements. Otherwise, screen readers waste time on irrelevant content.
What I got wrong
Early on, I wrote alt text like "SEO graph" for a chart showing keyword rankings over time. That told no one anything. Now I'd write: "Line graph showing keyword rankings improving from position 15 to position 3 over six months."
I also used to keyword-stuff product images. I had alt text like "red Nike running shoes size 10 buy now". It was spammy and didn't help anyone. Now I keep it clean: "Red Nike running shoes on a white background."
Next step
Quick answers
What is alt text?
Alt text (alternative text) is an HTML attribute added to an image tag that provides a text description of the image. It is used by screen readers for accessibility and by search engines to understand image content.
Does alt text help SEO?
Yes. Alt text helps search engines index images properly, which can improve visibility in image search results. It also contributes to overall page relevance when keywords are used naturally.
How long should alt text be?
Keep alt text under about 125 characters for optimal screen reader usability. For complex images like charts, provide a short summary in alt text and a longer description nearby.
Should I use keywords in alt text?
Yes, but only if they naturally describe the image. Avoid keyword stuffing, as it harms both user experience and SEO.
Sources
Primary documentation is linked directly. Anything commercial is marked nofollow.
- Google Search Central — Google's primary guidance on image indexing and image SEO best practices.
- WebAIM — Widely cited accessibility reference for writing effective alt text.
- W3C WAI — Standards-based guidance on the purpose and writing of alternative text.
- Google Search Central: Image SEO Best Practices — Useful for explaining how image metadata and context help Google understand images.
Notes from Callum Bennett.