What is alt text?
Alt text is the written description attached to an image, read aloud by screen readers and used by search engines to understand an image's content. Its primary purpose is accessibility; the SEO benefit is secondary.
It exists first for someone using a screen reader, who hears the alt text in place of the image. Writing it to describe what the image shows and why it's there, rather than to fit in keywords, serves that reader and any crawler equally well.
Its relevance to AI visibility follows from how most AI crawlers read a page: as text, without rendering it visually. An image with no alt text is not a poorly-described image to one of these crawlers, it is a blank space, indistinguishable from an image that was never there. For any page where the image carries real information, a chart, a product photo, a diagram, alt text is the only route that information has into an answer built from the page's text.
Related
- Server-side renderingServer-side rendering means the HTML arrives complete from the server. It matters because most AI crawlers do not execute JavaScript, so content injected in the browser is invisible to them.
- AI crawlerAn AI crawler is a bot operated by an AI company to fetch web pages for training, indexing, or answering a live question.
- Structured dataStructured data is machine-readable markup, usually schema.org JSON-LD, that states explicitly what a page and its subject are.
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