Alt text for SEO describes an image’s content to search engines that cannot see it, and to visually impaired users relying on screen readers. It serves both purposes simultaneously, and writing it well for one usually serves the other.
How to Write Good Alt Text
- Describe what is actually in the image, specifically – “red running shoes on a wooden floor,” not just “shoes.”
- Keep it concise, typically under 125 characters, since longer text may get truncated by screen readers.
- Include the target keyword only when it genuinely describes the image, never forced in when it does not fit.
- Skip “image of” or “picture of” – screen readers already announce that it is an image.
What to Avoid
Keyword-stuffing alt text with unrelated terms is both an accessibility failure and a spam signal search engines can detect. Leaving alt text entirely blank on meaningful, content-relevant images wastes a genuine ranking and accessibility opportunity – though purely decorative images should have empty alt text intentionally, not a forced description.
Alt Text vs Image File Names
Both matter and work together. A descriptive file name (“red-running-shoes.jpg” rather than “IMG_4521.jpg”) reinforces the same signal alt text provides, and the two should describe the same thing consistently.
Frequently asked questions
Do all images need alt text?
Content-relevant images need it. Purely decorative images (background textures, spacers) should have empty alt text (alt=””) so screen readers correctly skip them rather than announcing meaningless descriptions.
Does alt text directly improve rankings?
It primarily helps image search visibility and accessibility, and indirectly supports overall page relevance rather than acting as a strong standalone ranking factor for the page itself.
How is alt text different from image captions?
Alt text is invisible to sighted users and read by screen readers or search engines; a caption is visible text displayed near the image for all users. Both can exist on the same image with different purposes.
Serpwize checks alt text and image optimisation as part of every on-page SEO review. See our SEO outsourcing service.
