An alt tag is the written description attached to an image on a web page, used by screen readers to describe the image aloud and by search engines to understand what it shows. In code it is the alt attribute on an image element in HTML, which is why people also call it alt text.
Imagine reading a book to someone over the phone. When you reach a photo, you have to describe it for them, because they cannot see the page. That is exactly the alt tag’s job for a visitor using a screen reader: “Two engineers reviewing code on a laptop” tells them what a sighted user sees at a glance. This is a core part of web accessibility, working alongside ARIA attributes to make a site usable for everyone. It also acts as a fallback, showing the text if an image fails to load.
Good alt text is specific without being a novel. “Red trail-running shoe, side view” beats both a bare “shoe” and a sentence crammed with every keyword you could think of. For a button made of an image, describe the action (“Search”), not the picture, because that is what the person actually needs to do.
There is a clear SEO payoff as well. Google cannot see a picture, so the alt text is how it learns what the image contains, which helps it surface in image search and adds meaning to the surrounding content. Get it wrong and you fail twice over: a screen reader user hears noise, and a search engine learns nothing useful about the page.
At TopDevs we write accurate, useful alt text on every meaningful image, so a client’s site is accessible to all visitors and clearer to search engines at the same time.
