Adding alt text to media
Alt (alternative) text describes a media item and is an important part of a product description. If a media item can't load for any reason, then alt text is shown instead. It's also used by assistive technology to describe an image to a customer who's visually impaired. Including alt text can boost your website's SEO.
Keep your alt text brief and descriptive. The maximum length is 512 characters, but 125 or less is recommended.
You can also upload alt text in a CSV file.
From your Shopify admin, go to Products.
Click the name of the product that you want to edit.
From the product details page, click a product media item to see the Preview media page.
Click Add alt text.
Enter your alt text, and then click Save alt text.
Click the X to exit the preview page.