Alt Text

Featured image for an article about an alt text

Alt text is a written description added to an image through the alt attribute of an HTML img tag, describing the image content and purpose rather than displaying visible text on the page.

Alt text exists to make images accessible when they cannot be seen, whether because a screen reader is announcing the page to a visually impaired user, an image fails to load, or a search engine crawler is indexing the page content.

It differs from a caption, which is visible text displayed alongside an image for all readers, and from a title attribute, which typically appears as a tooltip on hover. It also differs from a file name, which is a technical label with no semantic role in the page.

In ecommerce, alt text is applied to product photos, banners, and blog images, and it factors into both web accessibility standards and image SEO.

Example

A dropshipping store selling a ceramic plant pot uploads a product photo with the file name IMG_4821.jpg. Without alt text, a screen reader would announce the file name, giving no useful information to a visually impaired shopper. The store owner adds alt text reading white ceramic plant pot with drainage hole, 6 inch diameter, so the image is understood by assistive technology and indexed correctly by search engines.

Key characteristics

Descriptive, not decorative: Alt text states what the image shows or does, not how it looks stylistically.
Concise: Most alt text runs under 125 characters so screen readers can announce it without truncation.
Keyword relevant, not keyword stuffed: A well-written alt text may include a natural product or topic keyword, but repeating keywords for ranking purposes is discouraged.
Empty when decorative: Purely decorative images use an empty alt attribute so screen readers skip them rather than announce irrelevant content.

Related terms

SEO – the broader discipline of optimizing a site for search visibility, of which alt text is one on-page element.
On-page SEO – the set of optimization practices, including alt text, applied directly to a webpage rather than external factors.
Search intent – the underlying goal behind a search query, which alt text can support when it matches how users search for images.

Frequently asked questions

Does alt text affect SEO?

Alt text can support SEO because search engines use it to understand image content, particularly in image search results, but it is not a major ranking factor for the overall page.

Is alt text the same as a caption?

No, alt text and captions are different: alt text is read by screen readers and search engines but is not visibly displayed, while a caption is visible text shown beneath or beside the image for every reader.

How long should alt text be?

Alt text is typically kept under 125 characters because most screen readers truncate or cut off longer descriptions, so shorter and specific phrasing works best.

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FAQ

Does alt text help with SEO?

Alt text supports SEO by giving search engines readable context for an image, and it can influence rankings in image search results specifically. Google has stated that descriptive alt text is one of several signals used to understand image relevance. It does not replace core SEO factors like page content or backlinks. Most SEO guidance recommends keeping alt text under 125 characters and specific to the image.

What happens if alt text is left blank?

When alt text is left blank, screen readers typically announce the image file name instead, which is rarely useful to the listener. Search engine crawlers also skip the image when ranking it for image search, since there is no descriptive signal to index. Studies on web accessibility estimate that a large share of ecommerce sites, sometimes cited above 30 percent, ship images with missing or empty alt attributes. This gap directly affects both accessibility compliance and search visibility.

Can alt text be too long?

Yes, alt text can be too long, and most screen readers truncate descriptions past roughly 125 characters. Search engines also give diminishing weight to alt text once it extends well beyond one short sentence. A common guideline is to keep alt text between 5 and 15 words, focused on the single most important detail. Overly long alt text can also read as an attempt to stuff keywords rather than describe the image.

Do decorative images need alt text?

Purely decorative images, such as spacers or background flourishes with no informational value, do not need descriptive alt text. Developers instead use an empty alt attribute, written as alt equals two quotation marks with nothing between them, so screen readers skip the image entirely. The Web Content Accessibility Guidelines, often cited as WCAG 2.1, specifically address this case. Around 1 in 4 websites tested in accessibility audits misuse this rule by leaving decorative images unmarked.

How is alt text different from a title attribute?

Alt text and a title attribute serve different purposes: alt text is read aloud by screen readers and displays if an image fails to load, while a title attribute shows as a small tooltip when a mouse hovers over the element. Alt text is considered essential for accessibility under WCAG 2.1, while title attributes are optional and not reliably read by assistive technology. Only about half of screen reader users report that hover tooltips are announced consistently. For that reason, alt text is the attribute prioritized for both accessibility and search purposes.