What Is Alt Text In SEO

Alt text in SEO is the written description placed inside an image’s HTML alt attribute. It functions as the image’s text alternative, used by screen readers when the picture cannot be seen and by search engines as one of the clearest signals for figuring out what the image shows.

The attribute makes images accessible to blind and low-vision users. It also gives crawlers the textual context needed to index and rank images. The rest of this guide breaks down how it works, why it matters, and how to write it well.

How the Alt Attribute Actually Works in HTML

The alt text lives in the alt attribute of the <img> tag. That attribute is the technical anchor for both accessibility and image SEO, which is why the W3C’s image tutorial for accessibility treats it as a required part of any non-decorative image.

One detail trips people up: alt="", an empty alt attribute, is a valid, intentional choice. When an image is purely decorative, an empty attribute tells screen readers to skip it entirely. The image stays visible to sighted users, but assistive technology no longer announces meaningless content. Both the W3C tutorial and MDN’s reference for the <img> element describe this as a deliberate accessibility pattern, not a missing field.

Title text is the attribute people confuse with alt text most often. The title attribute is optional, shows a tooltip on hover in some browsers, and is not read consistently by screen readers. It cannot replace alt text. Captions are different too: captions are visible text on the page, sitting below or beside the image, while alt text is invisible until the image fails to load or a screen reader reads it aloud. The same HTML basics show up in most on-page SEO guides built around modern publishing workflows.

Why Search Engines and Screen Readers Both Rely on It

Search engines and screen readers share a problem: neither can reliably see what is in an image. Pixels alone are not enough. Textual signals around and inside the image are how meaning gets communicated, and the alt attribute is the most direct signal of all.

Screen readers vocalize the alt text in place of the image. If a chart on a page shows rising sales, the alt text is how a blind user learns about that chart at all. WebAIM’s guidance on alternative text is built on this principle: alt text is the primary way non-text content reaches people who cannot see it.

Search engines read that same string as a description of the image’s subject. Google’s image best practices recommend descriptive alt text as a way to help Google Images understand the picture and match it to relevant queries. Because the same description helps both screen readers and crawlers, accessible images and well-indexed images are usually the same set.

How to Write Alt Text That Works in Practice

Good alt text describes the image’s purpose on the page, not every visible detail. The test is simple: read it aloud, and ask whether someone who cannot see the image would understand why it is there. A logo that links to the homepage, for instance, wants the brand name as its alt text, not a visual description of the symbol.

Keep it short and specific

Long alt text is usually bad alt text. A short, accurate sentence on a product photo beats a paragraph-long visual inventory every time.

Match the description to the image type

Different images ask for different alt text. The right wording depends on what the image is doing on the page.

• Product photos: name the product and a distinguishing feature such as color, use case, or angle, when that detail is what the page is selling.
• Charts and screenshots: summarize the insight or action, not the visual format. “Sales rose 18% in Q3 2024” is more useful than “bar chart.”
• Decorative graphics: use an empty alt attribute so the screen reader skips the image rather than announcing “blue squiggle” to the user.

Use keywords only when they fit

Keywords belong in alt text only when they are also the most accurate description of the image; otherwise, they get cut. Google’s guidance on writing good alt text is explicit on this point: accurate, descriptive text outperforms stuffed text on every front that matters, including rankings.

Common Mistakes That Undermine Alt Text SEO

Some teams still treat alt text as a place to park keywords. That habit usually traces back to older SEO advice, and it consistently produces worse outcomes for both accessibility and search. The alt attribute’s primary function is accessibility, and when writers ignore that, the descriptions become spammy, robotic, and unhelpful to screen reader users.

A related mistake is over-describing. Listing every detail a sighted viewer might notice, the colors, the angles, the background, the lighting, makes alt text longer without making it more useful. Effective alt text conveys the image’s purpose. If a chart’s job is to show a trend, the trend is what the alt text should say.

Teams also leave alt text empty for the wrong reasons: because a caption looks complete, or because the image “looks fine” to a sighted user. Neither holds up. Captions are visible supporting text that some readers skim, not a text alternative for the image itself. Skipping alt text on informative images leaves screen reader users and search engines without what they need.

Finally, reusing the same alt text across similar pages is tempting and usually wrong. Context changes meaning. The same product photo on a category page, a comparison page, and a holiday gift guide wants three different alt strings, each tied to that page’s angle. Repeated alt text loses relevance fast.

The Next Step for Better Alt Text

Alt text is a small detail that carries real weight: it serves screen reader users and search engines at the same moment, and it costs almost nothing to get right. Treat it as part of the publishing workflow rather than a final-pass chore.

Pick your most-visited page. Identify the informative images and the decorative ones. Write or rewrite the alt text on the informative images using the rules above, and set the decorative ones to an empty alt attribute. That single page, done carefully, will tell you everything you need to scale the same pattern across the rest of the site.