Good alt text describes what an image shows and why it is on the page, in one plain sentence. Write it for a person who cannot see the picture, and the SEO value follows on its own because search engines read the same text. Skip phrases like image of, describe the meaningful content rather than every pixel, and mark purely decorative images with an empty alt attribute so screen readers pass over them.
Alt text is one of those small details that quietly does two big jobs at once. It is the short written description you attach to an image, and it gets used in two moments that matter. When a blind or low vision reader moves through your page with a screen reader, the software reads that description aloud so they know what the image is. When a search engine crawls your page, it reads the same description to understand what the image shows, because software cannot truly see a picture either.
That overlap is the good news. You do not have to choose between writing for people and writing for search. When you describe an image honestly and clearly for someone who cannot see it, you have already given the search engine exactly what it needs. The trick is knowing what to say, what to leave out, and which images deserve a description at all.
Every image on a web page can carry an alt attribute, which is a piece of text tucked into the code that the visitor never normally sees. It surfaces in three situations. First, when a screen reader reaches the image, it speaks the alt text so the listener knows what is there. Second, if the image fails to load, the browser shows the alt text in its place. Third, search engines use it as one of the clearest signals of what an image represents, which feeds both regular search and image search.
Because the same text serves all three, alt text sits right where accessibility and SEO meet. This is why it matters so much for the overall health of a site. Get it right and you help real people while also giving search a cleaner picture of your content. Leave it blank or fill it with nonsense and you fail on both fronts at the same time.
The single most useful habit is to imagine reading your page aloud to someone over the phone. When you reach an image, what would you say so they understand it? That sentence, more or less, is your alt text. If the picture shows a chef pressing dough into a cast iron pan, then a chef pressing bread dough into a cast iron skillet is far more helpful than a vague label like cooking or a filename like IMG four four two one.
Keep it to about one sentence. You are giving the essential meaning, not narrating every shadow and color. Skip the words image of or photo of, because the screen reader already announces that it is an image, so those words just waste the listener's time. Describe the content and, where it matters, the purpose. A photo used to show a product looks different from the same photo used to illustrate a mood, and your description can reflect that.
Not every image needs a description. Some are purely decorative, like a background texture, a divider line, or a small flourish that adds nothing to the meaning of the page. For these, the correct move is an empty alt attribute, written as alt equals two quotation marks with nothing between them. That tells a screen reader to skip the image entirely, which keeps the experience smooth instead of interrupting the reader with pointless noise.
The mistake to avoid is leaving the alt attribute off completely. When it is missing, many screen readers fall back to reading the filename, so your listener hears a string of numbers and letters that means nothing. An intentional empty alt says skip this on purpose. A missing alt leaves the software guessing. The difference is small in the code and large in the experience.
Here is the part people get wrong. They treat alt text as a place to cram keywords, hoping to climb the rankings. It backfires. Search engines are good at spotting unnatural, repetitive alt text, and a listener using a screen reader is subjected to an ugly, meaningless phrase. Both outcomes hurt you.
The honest approach wins on both counts. Describe the image naturally, and if your target words genuinely fit the description, they will appear on their own. A page about choosing a stand mixer will have images whose true descriptions mention stand mixers, because that is what the pictures show. You get the relevance without the manipulation, and your images become eligible to appear in image search, which is a quiet extra source of traffic most sites ignore.
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Write the sentence you would say out loud, and you have served your readers and your rankings in one move. Your free website health check is at healthypage.help/check