Alt text (alternative text) is the written description you add to an image in HTML so that people using screen readers, search engines, and AI systems can understand what the image shows. It serves three audiences at once: a visually impaired visitor hearing the page read aloud, Google indexing your images, and increasingly an AI model trying to interpret your page. Get it right and one short sentence works for all three.
What every alt text guide tells you, and the piece they miss
Search “alt text” and you land on accessibility authorities: Harvard, Section508, WebAIM, Penn State, Microsoft. Their guidance is correct and we follow it. Be accurate, be concise (aim for around 125 characters, the point where screen readers tend to truncate), do not keyword-stuff, and leave purely decorative images with empty alt so screen readers skip them.
What those pages do not cover, because accessibility is their lens, is what changed for alt text in 2026: AI answer engines now read it. That is the part an SEO consultancy notices, and it is the reason this entry exists alongside the accessibility ones.
Alt text in the age of multimodal AI
Modern answer engines are multimodal. ChatGPT, Gemini, and Google AI Overviews interpret images alongside text, and alt text is one of the signals they use to understand what an image depicts and how it relates to the surrounding content. When your alt text accurately names what is in the image and ties it to the page topic, you are not only helping a screen reader, you are giving an AI model a clean, machine-readable caption it can trust.
This reframes alt text from a compliance checkbox into a small but real GEO signal. A page whose images are described precisely is more interpretable to a multimodal system than a page of unlabeled visuals. On client sites we now treat alt text as part of the content layer that AI engines parse, not just an accessibility requirement bolted on at the end.
How to write alt text that works for all three audiences
- Describe what matters, in context. “Bar chart showing organic traffic rising 40% after the 2026 content refresh” beats “chart.” The first serves a screen reader, gives Google Image context, and hands an AI engine a fact it can cite.
- Stay concise. Around 125 characters. Long descriptions get truncated by screen readers and add no value for machines.
- Skip the keyword stuffing. Cramming keywords harms the screen-reader experience and can be treated as manipulation. One natural mention of the relevant term is enough.
- Make each one unique. Multiple images on a page need distinct alt text so each is differentiated for both indexing and AI interpretation.
- Leave decorative images empty. An empty alt attribute tells assistive tech and crawlers to ignore a purely ornamental image.
How we check it
Google Search Console’s image performance data shows which images draw search traffic, which is the fastest read on whether your alt text is working for Image search. For coverage, a Screaming Frog crawl lists every image missing alt text across the whole site in one export, which is how we catch gaps at scale rather than spot-checking pages by hand.
FAQ
What is the ideal length for alt text? Aim for around 125 characters. That is roughly where screen readers truncate, and it is enough to describe the image accurately without padding. Decorative images should have an empty alt attribute instead.
Does alt text help SEO? Yes. It gives Google context to index and rank images in Image search, and it reinforces the page’s topic. In 2026 it also helps multimodal AI engines interpret your images, making it a small GEO signal as well as an SEO and accessibility one.
Do AI search engines use alt text? Yes. Multimodal engines like ChatGPT, Gemini, and Google AI Overviews read images alongside text, and accurate alt text gives them a reliable, machine-readable description of what an image shows and how it relates to the page.
Should decorative images have alt text? No. Purely decorative images should use an empty alt attribute so screen readers and crawlers skip them, avoiding wasted time for users and noise for machines.
