Alternative text (sometimes incorrectly called Alt tags) is text intended to describe something – typically images, audio and video – for those who can only read text. Typically this includes:
- Users with visual impairment, who have their webpages read out aloud to them.
- Search engines.
In particular, because search engines can’t understand images, audio and video like humans can, they are unable to index or find content hidden inside without ‘alternative’ text to look at. Including alternative text therefore is good SEO practice.
Whenever images, audio and video are used on the web, a text equivalent should be included. In most cases, this text equivalent is invisible to the ‘average user’, but is highly important to people with visual impairments and search engines. Consider the following image:
An image such as this should include a text equivalent, in this case “Apples” or “Two apples, one sliced in half” would be appropriate.
Alternative text is tested by the Alternative text test.