Alt text exists so people who cannot see an image still get its information. It also helps search engines understand images. Most sites either leave it blank or stuff it with keywords, and both fail.
Alt text should describe what the image conveys in context, in a sentence or less. Skip phrases like image of, since screen readers already announce it as an image. Leave alt empty for purely decorative images so screen readers skip them, and never stuff keywords, which is unhelpful to users and treated as spam.
What it is for
Primarily accessibility: screen reader users hear the alt text in place of the image. It also displays when an image fails to load, and gives search engines context about the image and the page.
Accessibility is the important one. In many jurisdictions missing alt text on informative images is a genuine compliance failure, not just a missed opportunity.
How to write it
| Image | Poor alt | Good alt |
|---|---|---|
| Team photo | team, staff, employees, company | Our six-person design team in the Manchester studio |
| Product shot | blue running shoe buy shoes online | Blue mesh running shoe, side view |
| Chart | chart | Bar chart showing enquiries rising from 4 to 19 per month over six months |
| Logo | logo | Acme Ltd |
| Decorative divider | decorative line |
For charts and diagrams, describe the finding rather than the format. Someone who cannot see it needs the information the chart carries, not a note that a chart exists.
When to leave it empty
Use an empty alt attribute, not a missing one, for images that carry no information: decorative dividers, background textures, spacer graphics.
An empty alt tells screen readers to skip the image. A missing alt attribute causes some screen readers to read the filename instead, which is usually worse than nothing.
Context changes the right answer
The same photograph needs different alt text depending on why it is there. On an about page, a photograph of your team might be described as the team. In an article about your new office, the relevant content might be the space itself.
The question to ask is what information would be lost if this image disappeared. That is what belongs in the alt text.
Common mistakes
- Starting with image of or picture of, which screen readers already announce.
- Keyword stuffing, which is unhelpful and treated as spam.
- Leaving the filename as alt text, so users hear IMG_4471.
- Writing alt text for decorative images, which adds noise.
- Describing an entire chart as chart, losing all its information.
Frequently asked questions
What is alt text?
A text description of an image, read aloud by screen readers and shown if the image fails to load. It makes images accessible to people who cannot see them and gives search engines context about what an image shows.
Does alt text help SEO?
Yes, modestly. It helps search engines understand images and is the main way images rank in image search. The stronger reason to write it is accessibility, which in many places is a legal requirement rather than an optimisation.
How long should alt text be?
Usually a sentence or less. Long enough to convey what the image communicates, short enough that a screen reader user is not stuck listening to a paragraph. Complex charts are the exception and may need a longer description elsewhere on the page.
Should decorative images have alt text?
No. Use an empty alt attribute so screen readers skip them. Leave the attribute present but empty rather than omitting it, since a missing attribute can cause the filename to be read aloud instead.
Is missing alt text a legal problem?
It can be. Accessibility standards such as WCAG require text alternatives for informative images, and those standards are referenced in accessibility legislation in many jurisdictions. Missing alt text on informative images is among the most commonly cited failures.