Alt Text Over 100 Characters: How to Write Better Alt Text

What this check flags

This audit item lists every image on your site whose alt attribute runs past 100 characters. Let's be clear up front, because a lot of tools are not: there is no rule in HTML, WCAG, or Google's documentation that says alt text must stay under any character count. The 100 to 125 character range is a usability convention, the same kind of soft threshold that axe flags as a best practice review item rather than a failure. We flag it because a long alt is almost always a symptom of something else, usually a caption dump, a keyword bag, or a description that belongs in visible page text.

Why length matters to a screen reader user

When a screen reader hits an image, it announces the alt text from start to finish. The user cannot pause halfway, cannot skim it, cannot jump to the next sentence inside the attribute. It is all or nothing: listen to the whole thing or skip the image entirely. Some screen readers, JAWS among them, even split very long alt text into multiple chunks, which makes one image sound like several. Now picture a 300 character alt attribute stuffed with comma separated keywords being read aloud, in full, in a monotone, to someone who just wanted to know what the picture shows. It is a fucking ordeal, and the person who wrote it never had to sit through it once.

Concise alt text is not about hitting a number. It is about respecting the listener's time.

What alt text is actually for

Alt text is a replacement for the image, not a commentary on it. It should convey the function or content of the image in its context: the same photo needs different alt text on a product page than in a news article. It is not a caption, not a photographer credit, not a metadata field, and absolutely not a container for your keyword list. Google's own image SEO documentation says to write useful, information rich text that uses keywords appropriately, and explicitly warns that stuffing keywords into alt attributes creates a negative user experience and can get your site treated as spam.

How to write good alt text

Ask one question: if the image disappeared, what short phrase would preserve the meaning of the page? Write that. Skip "image of" and "picture of" since the screen reader already announces it as an image. Be specific where specificity matters and silent where it does not.

<!-- Bad: 287 characters of keyword soup -->
<img src="boots.jpg" alt="best hiking boots, waterproof hiking
boots, hiking boots for men, cheap hiking boots, leather hiking
boots, buy hiking boots online, hiking boots sale, trail boots,
mountain boots, outdoor footwear, walking boots for sale UK">

<!-- Good: 52 characters, does the job -->
<img src="boots.jpg" alt="Brown leather waterproof hiking boot,
side view">

When a long description is legitimate

Some images genuinely carry more information than a sentence can hold: charts, graphs, diagrams, infographics. The answer is still not a 400 character alt attribute. Give the image a short alt that identifies it, then put the full explanation where everyone benefits from it.

Use the surrounding text

Describe the chart's takeaway in a visible paragraph right next to it, and keep the alt brief: alt="Bar chart of monthly organic traffic, described below". Sighted users get value from the prose too, and search engines can actually index it.

Use a structured long description pattern

For complex data, link to a description or data table, or use a <figure> with a detailed <figcaption>. The old longdesc attribute is obsolete in HTML and poorly supported, so prefer these visible patterns instead.

Decorative images: empty alt, not missing alt

If an image is pure decoration, a divider, a background flourish, an icon next to text that says the same thing, give it alt="". The empty attribute tells screen readers to skip it. Omitting the attribute entirely is worse: many screen readers fall back to reading the file name, and nobody needs to hear "IMG underscore 4 7 3 2 final final v 3 dot J P G".

How to diagnose

Crawl your site with any crawler that extracts the alt attribute, sort by length, and review everything over 100 characters by hand. For each one ask: is this describing the image, or dumping a caption, credit, or keyword list? Then spot check with a real screen reader, VoiceOver on a Mac or NVDA on Windows. Five minutes of listening to your own pages will recalibrate your idea of "reasonable length" permanently.

Common mistakes

Pasting the caption into the alt so the listener hears it twice. Stuffing keywords because someone in 2009 said it ranks. Describing every visual detail of a photo whose only job is decoration. Writing alt text for the image file instead of for its role on the page. And the quiet one: letting a CMS auto fill alt from the file name or product title and never reviewing it.

FAQ