Redundant alt text: image of, filenames and captions

What redundant alt text is

A screen reader announces an image as an image before it reads the alt. Starting the text with “Image of” or “Photo of” repeats that, and the user hears “image, image of a woman at a laptop”.

The other kind of redundancy is duplication. Alt text that repeats the caption underneath it, or the paragraph around it, gets announced twice. Alt text that is just the filename is worse: it is announced once and means nothing.

What squirrel checks

One check, image-redundant-alt, at severity warning. It reads every img[alt] with a non-empty alt and runs four tests. An empty alt, which marks a decorative image, is skipped.

• The alt matches one of 42 patterns. Those cover the prefixes image of, photo of, photograph of, picture of, graphic of, icon of, illustration of, diagram of, screenshot of, chart of, graph of, figure of and infographic of, the bare nouns on their own, logo, banner, img, thumbnail, hero image, cover image, featured image, placeholder, untitled, spacer, divider, and bare file extensions such as .jpg and .png.
• The alt matches the src filename. Both are lowercased and stripped of hyphens, underscores and spaces, and the filename must be longer than three characters. Item: alt="hero-banner" matches filename.
• The alt is repeated in the parent element’s text. This needs the parent’s text to be strictly longer than the alt and shorter than three times it, and the alt itself longer than ten characters, so a caption-sized repeat is caught while an exact-match parent and a long article are both left alone. Item: "Annual revenue chart..." duplicates surrounding text.
• The alt is repeated in a <figcaption>. The image has to be inside a <figure>, the alt longer than five characters, and the caption has to equal or contain it. Item: "Annual revenue chart..." duplicates figcaption.

Findings are deduplicated, then reported as N image(s) with redundant alt text, up to ten with a count of the rest. With nothing found the check passes as No redundant image alt text found, and a page with no alt at all returns info with No images with alt text found.

Elements inside <noscript> are skipped: a browser with scripting enabled reads <noscript> content as plain text, so nothing in it loads or renders. See content inside noscript.

How to fix it

<figure>
  <img src="q3-revenue.png"
       alt="Revenue rising from 4.1M to 6.8M between January and September">
  <figcaption>Q3 revenue</figcaption>
</figure>

Write what the image shows, not what kind of file it is. Where a caption already describes the image, the alt should add what the caption leaves out, or be empty if it adds nothing.

A logo whose correct alt is the company name, sitting in a file named after the company, trips the filename test. <img src="northwind.svg" alt="Northwind"> is right, and reported.

Enable / disable

Disable this rule

[rules]
disable = ["a11y/image-redundant-alt"]

Disable all Accessibility rules

[rules]
disable = ["a11y/*"]

Enable only this rule

[rules]
enable = ["a11y/image-redundant-alt"]

enable replaces the default ["*"], so this is the only rule selected. Leave disable out: a rule that matches any disable pattern is skipped even when enable names it. Only an enabled setting under a rule’s own [rule_options] table overrides both lists.

Related rules

• images/alt-text: images with no alt attribute at all.
• images/figure-figcaption: whether <figure> and <figcaption> are used correctly in the first place.
• a11y/input-image-alt: <input type="image">, which needs alt as a button name.
• images/filename-quality: whether those filenames are descriptive to begin with.

Accessibility findings ship in every audit next to the SEO, performance and agent experience rules. See Website security scan with AI for how an agent works through a report.

References

• The img element, MDN
• Understanding SC 1.1.1 Non-text Content, W3C
• Tips and tricks for images, W3C WAI tutorials

Check your site

Run squirrel audit https://example.com and open the Accessibility section of the report. Each finding says which of the four tests it tripped. Signed-out local audits need no account and cost nothing. Signed-in audits spend credits.