Why You Should Keep Alt Text Short and Succinct

You’ve probably heard that alt text should be short, no more than 150 characters. However, WCAG SC 1.1.1 Non text content states that “All non-text content that is presented to the user has a text alternative that serves the equivalent purpose,” but it doesn’t specify a character limit. Where does this 150 character limit come from, then?

The answer lies in how screen readers read alt text. Screen readers allow users to navigate around within a text with a lot of flexibility. In JAWS, you can do this with the Down Arrow and Up Arrow keys. Alt text, however, gets read in one chunk and can’t be paused. So if the alt text is long, that can make for a frustrating user experience. On a less technical note, shorter alt text eases cognitive load and can be less of an interruption to the text surrounding the alt text. When writing alt text, it’s also a good idea to include periods, even if the alt text is a sentence fragment. Screen readers pause briefly when they get to a period.