What is alt text?
Alt text, short for alternative text, is a written description of an image added in a page's code so that the meaning of the image is available when the image itself is not. It is read aloud by screen readers to people who are blind or have low vision, shown in place of an image that fails to load, and used by search engines to understand what an image depicts. Its first purpose is accessibility, making visual content usable by everyone, and a well-written description happens to help image search and on-page SEO at the same time because it communicates meaning rather than appearance.
Alt Text, explained properly.
What alt text actually is
Alt text is the alternative provided for an image so that its meaning survives when the picture cannot be seen. Technically it lives in the alt attribute of an image in a page's HTML, and it is not normally visible on screen. It surfaces in three situations. A screen reader announces it to a person who cannot see the image, so the description carries the information the picture would otherwise convey. A browser shows it when an image fails to load, so the page still makes sense. And a search engine reads it to work out what the image shows, since a machine cannot reliably interpret a photograph on its own. That first situation is the reason alt text exists. It is an accessibility feature before it is anything else, and treating it as a place to stuff keywords both fails the people who rely on it and undermines the very meaning search engines are trying to read. Good alt text simply describes the image in the context of the page, in plain language, as you would if you were describing it to someone who could not see it.
How to write good alt text
The test for good alt text is simple: if the image vanished, would the sentence you wrote leave the reader with the same understanding? That means describing what the image conveys in the context of the page, not cataloguing every visible detail. A product photo on a shop page is best described by what the product is, not by the studio lighting behind it. Length should be enough to carry the meaning and no more, because a screen reader has to read every word aloud. Phrases like image of or picture of are usually redundant, since assistive technology already announces that it is an image. Context changes the right description entirely: the same photograph might warrant different alt text on an article about architecture than on a page about a specific building, because the relevant meaning differs. Some images carry no information at all, being purely decorative, and those are best given empty alt text so a screen reader can skip them rather than announcing clutter. Text embedded inside an image, such as a heading baked into a banner, should be repeated in the alt text so it is not lost to anyone who cannot see it.
Why alt text matters for accessibility, SEO and image search
The primary case for alt text is accessibility, and for many organisations it is also a legal and ethical expectation rather than an optional extra. People who use screen readers depend on it to understand images that would otherwise be silent gaps in a page, and a site full of undescribed images is a site that quietly excludes them. The SEO benefit follows naturally from doing that well. Search engines use alt text as one of the main signals for understanding and ranking images, so clear, honest descriptions help your images surface in image search and add relevant context to the page they sit on. It also supports the broader machine understanding of a page, since alt text is one more place where the meaning of your content is stated plainly rather than left implicit in pixels. The important framing is that these goals point the same way. Writing alt text to genuinely describe an image for a person who cannot see it produces exactly the clarity a search engine rewards, whereas writing it to game rankings tends to produce descriptions that serve neither.
Common misconceptions
A few habits undermine alt text in practice. The first is treating it as a keyword field. Cramming search terms into the alt attribute degrades the experience for screen reader users and is exactly the kind of manipulation search engines have long discounted, so it fails on both fronts. The second is giving every image alt text regardless of purpose. Decorative images that add nothing to meaning are better left with empty alt text so assistive technology can skip past them, and describing them only adds noise. The third is confusing alt text with other fields. The title attribute, the file name and the caption all play different roles, and none of them replaces a proper description in the alt attribute. The fourth is assuming alt text is only an SEO tactic. It is an accessibility requirement that also happens to help SEO, and framing it the other way round tends to produce worse writing. The reliable approach is to describe each meaningful image honestly, in context, and let the search benefit follow from having done the accessible thing well.
Alt Text: common questions.
What is alt text in simple terms?
Alt text is a short written description of an image, added in the page's code, so that the meaning of the image is still available when the image itself is not. It is read aloud by screen readers to people who cannot see the image, shown in place of an image that fails to load, and read by search engines to understand what the image shows. In plain terms, it describes a picture for anyone, or anything, that cannot see it.
Is alt text mainly for accessibility or for SEO?
Primarily accessibility. Alt text exists so that people who use screen readers can understand images, and for many organisations providing it is an ethical and often legal expectation. The SEO benefit is real but secondary: search engines use alt text to understand and rank images, and clear, honest descriptions help. The two goals align, because describing an image genuinely well for a person who cannot see it produces exactly the clarity a search engine rewards.
How long should alt text be?
Long enough to convey the meaning of the image and no longer. A screen reader reads every word aloud, so padding becomes a burden for the people who rely on it. Describe what the image communicates in the context of the page rather than every visible detail, and skip phrases like image of, since assistive technology already announces that it is an image. If a single clear sentence carries the meaning, that is usually enough.
Should every image have alt text?
Every image that carries meaning should, but purely decorative images are the exception. If an image adds nothing to understanding, such as a background flourish or a divider, it is better given empty alt text so a screen reader skips it rather than announcing noise. The judgement is whether the image conveys information a reader would otherwise miss. If it does, describe it. If it is there only for looks, let assistive technology pass over it.
Should I put keywords in my alt text?
No, not as a tactic. Alt text should describe the image honestly, and if a relevant term naturally belongs in that description then it fits. Deliberately stuffing keywords degrades the experience for screen reader users and is the sort of manipulation search engines discount, so it fails on both counts. Write the description you would give to someone who could not see the image, and any search benefit follows from having genuinely conveyed what the image means.