What Is Alt Text and How to Write It for SEO

Alt text (short for alternative text) is a written description of an image that lives in the image’s HTML alt attribute. It is not usually visible on the page, but it does two important jobs: it is read aloud by screen readers so people who cannot see the image still understand it, and it helps search engines figure out what a picture shows. Learning how to write alt text well is one of the easiest on-page wins available, because it improves accessibility and SEO in the same small step.

What alt text is for

The primary purpose of alt text is accessibility. People who use screen readers rely on it to know what an image contains, whether that image is a product photo, a chart, or a decorative flourish. If the image fails to load, the browser also shows the alt text in its place, so a reader still gets the meaning. Search engines cannot truly “see” a picture the way a person can, so they lean on alt text, the file name, and surrounding content to understand and index it.

How alt text helps SEO

Alt text gives search engines readable context for an image, which helps that image appear in image search and can add relevance signals to the page overall. Well-described images are more likely to surface in Google Images, which is a real traffic source for many topics. Alt text also strengthens the topical clarity of a page, working alongside your headings, body copy, and internal links. It is a supporting on-page signal rather than a ranking lever — part of the same toolkit covered in our on-page SEO best practices checklist.

There is a second, quieter benefit worth noting. Alt text pairs with a descriptive file name and the caption or text around the image to give search engines a fuller picture of what the visual shows. None of these alone is powerful, but together they help an image be understood correctly, which matters when your pictures are genuinely useful — product shots, diagrams, screenshots, or charts that a searcher might be hunting for directly.

How to write good alt text

Aim to describe the image clearly and concisely, in a way that would make sense if it were read aloud. A few practical rules:

• Describe what the image actually shows, in plain language, usually in a short sentence or phrase.
• Include a relevant keyword only if it fits naturally — never force it.
• Skip “image of” or “picture of”; screen readers already announce that it is an image.
• Keep it reasonably short; very long alt text becomes tiring when read aloud.
• For photos of text (like a quote graphic), put the actual text in the alt attribute.

Should decorative images have alt text?

Not always. If an image is purely decorative and adds no information — a background texture or a divider line, for example — the accessible approach is to give it an empty alt attribute (alt=""). An empty alt tells screen readers to skip the image, which is better than making a user listen to a description of something meaningless. The key distinction is whether the image conveys information the reader needs. If it does, describe it; if it is purely visual decoration, an empty alt is correct and intentional.

What is the difference between alt text and a caption?

Alt text and captions are not the same thing. Alt text lives in the HTML and is generally invisible; its job is to describe the image for people who cannot see it and for search engines. A caption is visible text displayed near the image for everyone to read, often adding context, credit, or commentary. The two can overlap, but they serve different audiences. You should still write proper alt text even when an image already has a visible caption, because the caption does not sit in the alt attribute and screen readers may handle them differently.

Does every image need alt text?

Every meaningful image should have alt text, and every decorative image should have an empty alt attribute so it is deliberately skipped. In other words, no image should simply be missing the attribute — you should always make a conscious choice between describing it and marking it as decorative. Content images, product photos, infographics, and charts all deserve accurate descriptions. Missing alt text is a common accessibility problem and an easy one to fix during a routine content review, right alongside checking headings and title tags and H1s.

Common alt text mistakes to avoid

The most frequent mistakes are leaving alt text blank on informative images, stuffing it with repeated keywords, and writing vague descriptions like “photo1”. Keyword stuffing in alt text is unhelpful for readers using screen readers and can look manipulative to search engines. Copying the same alt text across many different images is another miss, since each image should be described on its own terms. A quick test helps: read your alt text aloud and ask whether it would tell a listener what the image shows without seeing it. If the answer is no, rewrite it.

Treat alt text as writing for a person who cannot see the screen — get that right, and the SEO benefit follows naturally. It costs almost nothing to add during publishing, yet missing or careless alt text is one of the most common issues found in content audits. If you are building a broader picture of on-page relevance, pair strong alt text with content that matches search intent.