Alt text, or alternative text, is a sentence or phrase that is used to tell readers the contents of an image, as it relates to the document subject. In online documents, alt text is useful when an image link is broken or otherwise not available.
When a content creator inserts an image into their document, alt text is created as an attribute of the image element (tag). For example, if a content creator inserts an image of a dog, the alt text might describe the breed and characteristics of the dog if the document is about dog breeds, or it might list the name, age, and behavior of the dog if it is a document about that specific dog.
Note that alt text is different from image descriptions. While alt text should tell viewers as much as possible about the image in as few words as possible, image descriptions are meant to provide a more detailed description:
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Alt text
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Image Description
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Short, condensed sentence or phrase
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Longer, more detailed description
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Summary of the image
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More information about the subject of the image
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Alt text is not necessary for images that are meant to indicate application or site navigation, such as small-image buttons, or decorative images.
Alt text is helpful for improving search engine optimization (SEO) for your document or website, as you can include searchable terms and keywords in the descriptive text.
Alt text is important for accessibility. Screen readers require alt-text to describe the image for those who can't see it.
