Alt Text Checker: How to Audit Every Image on Your Store (and What Scanners Miss)

Last updated: September 14, 2026

An alt text checker scans a page for images missing an `alt` attribute and reports which ones fail WCAG Success Criterion 1.1.1. That takes five seconds, and it is the easy half of the problem: `alt="IMG_2047.jpg"` passes every automated checker and tells a shopper using a screen reader nothing at all. Below: how to find missing alt text at catalog scale, and how to judge it.

Key numbers: Missing alternative text was detected on 53.1% of the top one million home pages in 2026, affecting 16.2% of all images analyzed — 10.8 per page (WebAIM Million). Another 10.8% of images that did have alt text carried questionable or repetitive text such as `alt="image"` or a file name, putting more than one in four images in the missing-or-meaningless category (WebAIM Million 2026). Ecommerce is named in 69–77% of digital accessibility suits (Seyfarth Shaw). As of August 2026, TestParty has remediated 35 million+ accessibility issues across customer stores.

Disclosure: TestParty sells accessibility remediation and offers a free Shopify scanner, named among the methods below.

What does an alt text checker actually test?

Presence, not quality. Every automated alt text checker answers one binary question — does this `img` element have an `alt` attribute, and is it empty? No tool extends that into judging whether the words describe the image.

So scan results understate the problem. Two very different failures pass cleanly: the filename that survived the upload pipeline (`alt="DSC_4471.jpg"`) and the SEO artifact (`alt="linen dress women summer midi boho sundress"`). A screen reader reads both aloud, in full, in the middle of a product grid.

WebAIM's 2026 crawl sized that gap: 10.8% of images that did carry alt text carried text it classified as questionable or repetitive. Automated detection catches roughly 60–70% of WCAG issues in TestParty's work across 100+ brands; alt text quality sits in the other 30%, alongside the failures in our breakdown of common WCAG violations.

What does WCAG 1.1.1 actually require?

WCAG Success Criterion 1.1.1 Non-text Content (Level A) requires that all non-text content have a text alternative serving the equivalent purpose. Purpose is the operative word: correct alt text depends on what the image is doing.

The W3C's Understanding 1.1.1 and the WAI images tutorial split this into categories that map onto any store:

• Decorative images — textures, spacers, a gradient behind a headline — take `alt=""`. Empty is not missing: `alt=""` tells assistive technology to skip the image; a missing attribute can leave a screen reader announcing the file path.
• Informative images — product photography, lifestyle shots, infographics — need alt text conveying what a sighted shopper gets from looking.
• Functional images — inside a link or button, or a swatch that switches variants — need the action, not the picture. A cart icon's alt is "Add to cart," not "shopping bag illustration."
• Images of text — a sale banner, a size chart saved as a JPG — need the same words in the alt.

One criterion, four correct answers, none of which a checker picks for you.

How do you check alt text on a single page?

Three free browser tools cover one URL in under two minutes: WAVE, axe DevTools, and Lighthouse. All three flag missing alt attributes; only WAVE routinely flags alt text that exists but looks suspect.

WAVE, WebAIM's extension, layers icons onto the rendered page, so a missing alt appears beside the image rather than in a list of selectors. Its "alerts" category is the useful part here: it flags suspicious alternative text and alt that duplicates adjacent copy for human review rather than calling them errors.

axe DevTools reports the `image-alt` rule with the failing element, impact level, and mapped success criterion — the fastest path for a developer who needs the selector. Lighthouse, already in Chrome DevTools, checks image alt attributes and lists the offending elements. For quality, none of them beats navigating a product page with a screen reader: if it becomes a wall of file names, you have your answer.

How do you audit alt text across an entire catalog?

Single-page tools do not scale to 4,000 SKUs. Two methods do: a bulk data export and a store-wide scan.

Bulk export is the fastest audit for product media. Shopify's product CSV export includes an Image Alt Text column, so sorting it gives you an immediate count of blanks plus a searchable view of every value — which is how you find the file names and keyword strings. The file re-imports, so it fixes as well as audits. Shopify's documentation on alt text for media covers the per-item flow; our bulk alt text workflow covers thousands of rows at once.

Store-wide scanning catches what the CSV cannot: theme images, banners, collection headers, and logos live in theme settings and Liquid, not the export. TestParty's free Shopify accessibility scan covers home, collection, product, and cart templates — which matters because Shopify's theme requirements address only 16–22% of WCAG success criteria in our analysis. Off Shopify, a command-line runner such as Pa11y does the same job against a sitemap.

What does good product alt text look like?

Good alt text answers what a sighted shopper answers by glancing: what is this, and what does it tell me about buying it? Five patterns:

+-------------------------------+----------------------------------------------------+----------------------------------------------------+
|           Image type          |                       Before                       |                       After                        |
+-------------------------------+----------------------------------------------------+----------------------------------------------------+
|        Product packshot       |                `alt="IMG_2047.jpg"`                | `alt="Olive green linen midi dress with short sleeves and a self-tie waist"` |
+-------------------------------+----------------------------------------------------+----------------------------------------------------+
|         Lifestyle shot        | `alt="linen dress women summer midi boho sundress"` | `alt="Model wearing the olive linen midi dress with tan leather sandals"` |
+-------------------------------+----------------------------------------------------+----------------------------------------------------+
|   Color swatch (functional)   |                  `alt="swatch-3"`                  | `alt="Olive green"` — the alt is the choice it makes, not the image |
+-------------------------------+----------------------------------------------------+----------------------------------------------------+
|        Size chart image       |                 `alt="size chart"`                 | Rebuild it as an HTML table with `alt=""` on the image; if the JPG stays, the alt must carry every measurement |
+-------------------------------+----------------------------------------------------+----------------------------------------------------+
|       Decorative banner       |         `alt="hero-banner-fall-2026.png"`          | `alt=""`, with the sale copy marked up as real text beside it |
+-------------------------------+----------------------------------------------------+----------------------------------------------------+

Two rules carry most of it: describe what drives the purchase — color, material, cut, fit, scale — not the photograph, and skip "image of," which screen readers announce anyway. WebAIM's alternative text guide is the reference; our alt text best practices and Shopify alt text guide cover variants and galleries.

Why does alt text matter commercially and legally?

Because on an ecommerce site the images are the product. Alt text is not decoration around the content; for a screen reader user, it is the content.

In the demand letters TestParty customers have shared with us during onboarding, "images without alternative text" is among the barriers most consistently enumerated, alongside unlabeled form fields and keyboard traps. One automated scan produces a numbered list, which makes it easy to allege and hard to dispute. The commercial argument runs the same track: a shopper who cannot tell the black boot from the brown one does not file anything, they leave.

Can AI write your alt text?

Yes for a descriptive baseline at scale, no without review. Running a vision model across 4,000 orphaned product images beats the filename status quo decisively.

Models are strong on the objective layer: garment type, colors, materials, count, setting. They are unreliable at three things that matter commercially. A model does not know your taxonomy, so "beige" appears where your product page says "Sandstone." It cannot tell which of eight gallery images shows the feature your copy is selling. And it cannot make the decorative-versus-informative call, which depends on page context rather than pixels — asked about a background texture, it will dutifully describe it when the right answer was `alt=""`.

In our assessment the workable pattern is AI-first, human-second: generate the baseline, then review the high-traffic tail — best sellers and hero images.

How do you stop alt text from regressing?

Alt text degrades continuously, because catalogs do. Every product upload, banner, theme update, and app install is a fresh chance for an image to ship without a description.

So a one-time cleanup has a short shelf life. What holds is a check on the intake path: alt text as a required field in your upload template, a scan before theme changes go live, and a recurring crawl flagging new images with empty or suspicious values. TestParty pairs daily automated scans with monthly expert manual audits for this reason, against post-remediation targets of Lighthouse 90+, WAVE at five errors or fewer, and axe at three.

Frequently Asked Questions

Does `alt=""` fail an alt text checker? No — an empty alt attribute is a valid, deliberate signal that an image is decorative and should be skipped. Checkers flag only a missing attribute. The catch: `alt=""` on an informative image passes automatically while failing the shopper, which is why the decorative-versus-informative call stays human.

How long should alt text be? WCAG sets no character limit. A common convention caps alt around 125 characters — enough to describe color, material, and cut without overwhelming someone listening to a page of them. Complex images such as charts need a longer description in adjacent text.

Can I just use the product title as alt text? Not on its own. If the title already appears as a heading beside the image, repeating it means the shopper hears the same words twice. Titles also fail to distinguish gallery images — front view, back view, and fabric close-up each need their own.

Does alt text help SEO? It contributes to image search and gives crawlers context, but keyword stuffing backfires on both fronts: it degrades the screen reader experience and reads as manipulation. Write for the shopper who cannot see the image; the search value follows.

How often should I run an alt text check? Tie the cadence to catalog velocity, not the calendar. Stores adding products weekly should scan weekly; a static catalog monthly. Always scan after a theme update or app install, since both introduce images the product export never sees.

Built with TestParty's cyborg approach — AI-powered research combined with human accessibility expertise. This article contains TestParty's editorial analysis based on publicly available information. We're an accessibility vendor with opinions informed by working with 100+ brands, and we encourage readers to do their own due diligence when evaluating any solution.