Alt Text
Alt text is a text alternative that communicates the purpose or meaning of an image when the image itself cannot be perceived.
In HTML, it is commonly provided through the alt attribute of an image.
What It Means in Practice
Good alt text is not necessarily a literal description of everything visible in an image.
Its job is to provide the information the image contributes in its specific context.
The same image may need different alt text in different situations.
An image that adds no meaningful information may instead need an empty alt attribute so a screen reader can ignore it.
How It Works
For an informative image, the alt attribute can contribute the image's accessible name.
A screen reader can then announce the text alternative instead of requiring the user to see the image.
Complex information such as charts may require additional explanation beyond a short alt attribute.
Why It Matters
Images can carry information that is unavailable to someone who cannot see them.
Without an appropriate text alternative, important instructions, context, data, or meaning may disappear entirely.
Common Problems
Common alt-text issues include:
- Missing alt attributes
- Describing decorative images unnecessarily
- Writing filenames as alt text
- Beginning every description with “image of”
- Describing appearance while missing the image's actual purpose
- Trying to fit complex charts into a single short description
How to Improve
Ask:
What information would be lost if this image were unavailable?
Write the alternative around that answer.
Decorative images should generally be hidden appropriately from assistive technologies rather than described for the sake of filling the field.