Alt text is the written description in an image's HTML alt attribute for screen readers and crawlers

What is alt text?

Alt text (alternative text) is the written description placed in an image's HTML `alt` attribute. It is read aloud by screen readers for accessibility and parsed by search engine and AI crawlers to understand what an image depicts, since crawlers cannot "see" images.

In HTML it looks like this:

`<img src="golden-retriever-puppy.jpg" alt="Golden retriever puppy sitting on grass">`

The text inside the quotes after `alt=` is what a screen reader announces and what a crawler reads as the image's meaning. If the image fails to load, the browser displays this text in its place.

Alt text vs alt attribute vs alt description: are they the same thing?

These three terms describe the same thing from different angles. "Alt attribute" refers to the HTML attribute itself (`alt=""`), "alt text" is the content written inside it, and "alt description" is a plain-language synonym people use for the same content. There is no functional difference between them; the term you choose depends on whether you are talking about code, content, or the concept in general.

Why does alt text matter for accessibility and SEO?

Alt text matters because it makes visual content usable for people who cannot see images and understandable for machines that cannot interpret pixels. Screen reader users rely on alt text to know what an image shows, which is a core requirement under WCAG (Web Content Accessibility Guidelines). Search engines use alt text as a ranking signal for image search and as supporting context for the surrounding page content, which is why missing alt text is a standard finding in a technical SEO audit or site audit.

How do AI answer engines use alt text?

AI answer engines like ChatGPT, Perplexity, and Google AI Overview use alt text as one of the few direct signals they have about what an image contains, since they cannot visually inspect it the way a human can. When these engines crawl a page (via bots such as GPTBot or Google's crawlers) to generate an answer or display an image citation, they combine the alt text with surrounding headings, captions, and body copy to decide if the image is relevant enough to reference. Pages with accurate, descriptive alt text give AI crawlers more reliable material to work with, which supports broader AI visibility and citation in tools tracked under ai-search-engine-optimization and generative-engine-optimization strategies. This applies alongside other crawler access signals such as llms.txt and robots.txt rules for AI bots.

How do you write good alt text?

Good alt text describes what the image shows in plain, specific language, without restating that it is an image. Follow these rules:

• Be concise: aim for roughly 8-15 words, enough to convey the content without padding.
• Be specific: describe the subject, action, and relevant detail ("Woman typing on a laptop at a standing desk" beats "Person working").
• Skip "image of" or "picture of": screen readers already announce that it's an image, so this phrasing is redundant.
• Use keywords naturally, only if they genuinely describe the image; do not force unrelated terms in.
• Leave `alt=""` empty for purely decorative images (dividers, background textures) so screen readers skip them.

How long should alt text be, and how should it be formatted?

Alt text should generally stay under 125 characters, since many screen readers cut off longer descriptions. Write it as a plain descriptive phrase or short sentence, without markup, hashtags, or keyword lists. For complex images like charts or infographics, put a short summary in the alt attribute and a fuller explanation in the surrounding text or a caption.

Can an alt text generator write good alt text automatically?

An alt text generator uses image recognition to produce a draft description automatically, which is useful for large image libraries or e-commerce catalogs where manual writing at scale is impractical. Automated tools are generally accurate for simple, literal descriptions (a red shoe, a mountain landscape) but often miss context that only a human knows, such as why an image matters on that specific page or what brand terminology to use. The safest approach is to use a generator for first-pass coverage and manually refine alt text for high-value pages, product images, and anything used in content strategy or programmatic content.

What are common alt text mistakes to avoid?

The most common mistakes are leaving the alt attribute blank on meaningful images, stuffing it with repeated keywords, writing generic text like "image1.jpg," and describing decorative images that add no informational value. Keyword stuffing in alt text can look manipulative to search engines and adds no value to screen reader users, so it should be avoided even when the goal is image SEO.

Do I need alt text for every image?

No. Purely decorative images, such as spacer graphics or repeated background patterns, should use an empty `alt=""` so assistive technology skips over them. Every image that conveys information, including logos, product photos, charts, and screenshots, needs descriptive alt text.

How is alt text flagged in a technical SEO audit?

A technical SEO audit crawls every page and checks whether each `<img>` tag has a populated, non-generic alt attribute, flagging missing or empty alt text as an on-page issue to fix. Across the 874 websites SeoVision has audited (as of 2026-08-12), the median on-page SEO score is 75/100, and missing or weak alt text is one of the recurring issues that pulls scores down in that category, alongside gaps covered in a broader website SEO check or SEO auditor review.

How SeoVision checks this

SeoVision's free site audit checks this on every page it crawls, including titles, meta tags, headings, and image alt text, and turns what fails into a prioritized action plan. Across the sites it has audited, SeoVision's median AI readiness score is 83/100, reflecting how much room most sites still have to make their content, including images, easier for AI crawlers to interpret. Run a free site audit to see exactly which images on your site are missing alt text and how it affects your SEO and AI readiness scores.