What is an Alt Tag? An alt tag or alt company email list is a type of HTML text that contains information telling users and crawlers that there is an image present on the web page, and information about that image. Why are Image Alt Tags Important? Alt tags are important for a range of reasons. 1. They Improve Accessibility Alt tags can help users that are visually impaired and using voice readers to discover and understand the images that are embedded within web page content.