Alt Text SEO
Describes an image's content or function in HTML so screen readers and search engines can understand it when the image is unavailable.
If you have ever stuffed keywords into alt text hoping for a ranking boost, you already know it hurts both usability and your image SEO.
Key points
- Write alt text for people who cannot see the image, not for search engines.
- Keep it under roughly 125 characters for screen-reader usability.
- Use an empty alt attribute for purely decorative images.
- Describe the image's purpose in context, not just its literal appearance.
- Avoid phrases like 'image of' or 'picture of' — they are redundant for screen readers.
- Do not duplicate nearby text if the same information is already in the caption or body copy.
A product image with and without keyword stuffing
An e-commerce site sells a 'blue ceramic mug'. The alt text reads 'buy blue ceramic mug online cheap best price mug for coffee tea gift.' That is keyword stuffing — it is hard to read and hurts usability. A better version: 'Blue ceramic mug on a wooden table, filled with coffee.' That describes what the image shows, stays under 125 characters, and naturally includes the key term 'blue ceramic mug' without forcing it.
Three situations where this changes your decision
- Meaningful vs decorative images A meaningful image needs descriptive alt text; a decorative image should use an empty alt attribute (alt="") so screen readers skip it.
- Complex images like charts A chart or graph needs a short alt text summary plus a longer description or a nearby data table for full accessibility.
- Images with captions If the caption already describes the image fully, alt text can be brief or empty to avoid repetition.
Four ways it goes wrong
- Blank alt for meaningful images Leaving alt text blank on a meaningful image means screen readers announce the filename or nothing, which is a core accessibility failure.
- Keyword stuffing Forcing exact-match keywords unnaturally makes alt text unreadable and is discouraged by Google Search Central and WebAIM because it harms both usability and search performance.
- Vague descriptions Writing 'image' or 'photo' instead of a useful description gives no context to users or search engines, wasting the opportunity to improve accessibility and image SEO.
- Repeating surrounding text Copying the caption or body copy verbatim into alt text adds no new information and wastes a chance to provide unique context.
What to check before writing alt text
- Is the image meaningful? If the image conveys information, it needs descriptive alt text. If it is purely decorative, use an empty alt attribute.
- What is the image's purpose? Describe what the image does in context — a logo links to the homepage, a product photo shows the item's appearance.
- Is the alt text human-reviewed? Automated or unedited generated alt text often misses context; human review is preferred for both accessibility and SEO.
Common questions
What is alt text for images?
Alt text is the HTML text alternative that describes an image's content or function for screen readers and search engines.
How to write alt text for images?
Describe the image's purpose in context, keep it under 125 characters, avoid keyword stuffing, and skip phrases like 'image of'.
Does alt text help SEO?
Yes, it helps search engines understand image context and can support image search visibility, but it is primarily an accessibility practice.
Sources
- Google Search Central Official guidance on image SEO and alt text best practices.
- WebAIM Detailed techniques for writing effective alt text for accessibility.
- W3C WAI W3C tutorial on image accessibility, including decorative and complex images.