An image’s alt text is a single sentence, yet it is the sentence most often rushed. Here are the rules that make the difference, with before/after examples you can apply today.
What is alt text for?
- It is read by screen readers, which let blind and visually impaired people understand the image.
- It is displayed in place of the image when the image fails to load.
- It helps search engines understand what the image shows.
The rules of good alt text
- Describe what is visible, in one sentence, as if you were describing it over the phone.
- Stay short: around 125 characters, the usual recommendation for screen readers.
- Do not invent places, brands or promises that are not in the image.
- Skip “image of” or “photo of”: the screen reader already announces it is an image.
- Write in the language of the page where the image appears.
- Think about the image’s function: for an image that works as a link, describe the destination or the action, not the drawing.
Before / after
- File name — before: “IMG_2024.jpg”; after: “White ceramic mug on a light wooden table.”
- Too poor — before: “mug”; after: “White ceramic mug with a rounded handle.”
- Keyword stuffing — before: “cheap mug ceramic buy white mug sale”; after: “White ceramic mug with a rounded handle.”
- Image link — before: “logo”; after: “Back to the Toitures Martin home page”
- Project photo — before: “job site”; after: “Roofer laying slates on a pitched roof.”
When to leave the alt text empty
A purely decorative image (a rule, a pattern, an illustration that repeats the neighbouring text) should have an empty alt attribute, not a missing one: an empty alt tells the screen reader to move on, whereas a missing alt may make it read out the file name.
Special cases
- Charts and infographics: a short alt that states the subject, and the detailed data in the text next to it.
- Images that contain text: repeat that text in the alt.
- Product photos: colour, material, view, visible use. Keep sales arguments for the product page.
And when you have thousands of images?
Writing by hand is fine for a few dozen images. Beyond that, an extension like SafeAlt writes the alt text, title and caption of each image with AI. Always review your important images: an AI can be wrong about what it sees.
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