How to check missing alt text on your website (free tools and methods)

You run an SEO audit on your shop and, buried in the report, there are 340 images flagged as missing alt text. You know it matters for accessibility and search rankings — but where do you even begin? An image alt text checker is the fastest way to see the full picture before touching a single file. This guide covers four methods, from a thirty-second browser trick to a full automated crawl, so you can choose what fits your situation.

How to find missing alt text with browser DevTools

Every modern browser ships with developer tools you can open right now. They give you per-image inspection without installing anything.

Inspecting a single image:

1. Right-click the image on the page and select "Inspect" (or "Inspect Element").
2. The DevTools panel opens with the <img> element highlighted.
3. Look for the alt attribute in the HTML. Missing entirely, or set to alt="" on a meaningful image, both signal a problem.

For a broader sweep, open the browser Console tab and paste this one-liner:

document.querySelectorAll('img:not([alt])').length

That returns the count of images with no alt attribute at all. To list the src values of every offending image:

[...document.querySelectorAll('img:not([alt])')].map(i => i.src)

This approach works on any page you can load in a browser. The limitation is that it checks only the current page, and it only catches missing alt — not empty or meaningless alt text like "image" or "IMG_4821".

Free browser extensions for alt text checking

Browser extensions give you a visual overlay on the page so you can spot problems without touching the console. Several are worth knowing.

Web Developer (Chris Pederick): Available for Chrome and Firefox, this extension has a dedicated "Images" submenu. "Outline images without alt attributes" draws a red border around every offending image. "Display alt attributes" shows the alt value as a tooltip over each image. It is not subtle — it is the fastest way to eyeball a page.

axe DevTools (Deque): The free tier of the axe extension runs a full WCAG check, including missing alt text, and highlights issues with colour-coded overlays. It reports alt text failures under WCAG criterion 1.1.1. It covers far more than alt text — contrast failures, missing form labels, and focus management issues all surface in the same scan.

WAVE (WebAIM): WAVE injects icons into the page to flag errors and warnings. A red icon marks each image with a missing alt; a yellow icon marks images where the alt text may be insufficient (for example, alt text that matches the file name). Click any icon to read the explanation.

None of these extensions store data or require accounts. The trade-off is that you are checking one URL at a time. For a store with 200 product pages, that is not practical.

Online WCAG scanners

Online scanners send a URL through an automated engine and return a structured report — no extension, no setup. They cover far more than just alt text, which makes them useful for understanding your compliance position overall.

Altvisor's free WCAG checker scans a URL against WCAG 2.1 AA criteria. The results include missing alt text, colour contrast failures, missing form labels, keyboard navigation gaps, and a compliance score. It renders the page with a real browser, so JavaScript-rendered content (including product images loaded dynamically) is included in the scan. A single free scan takes under 60 seconds.

Other widely-used free scanners include the W3C Nu HTML Checker (code validation rather than WCAG), WAVE's online version (the same engine as the extension), and Accessibility Insights from Microsoft (a desktop application that runs a more thorough audit than a browser extension).

Worth noting: automated scanners reliably catch between 30 and 40 percent of WCAG issues. Missing alt text falls well within what automation handles well. Problems like unclear link text, poor heading structure, and keyboard focus management in custom components require a human tester. Treat the automated report as a starting point, not a certificate.

Automated crawlers for larger sites

When your site has hundreds or thousands of pages, you need a tool that follows links and builds an inventory. Two desktop crawlers are standard in this space.

Screaming Frog SEO Spider: The free version crawls up to 500 URLs. It exports a spreadsheet of every image found, including the alt attribute value and a flag for missing or empty alt text. It also reports image file size, dimensions, and the pages where each image appears. For a single export of all image issues, go to the Images tab after the crawl completes, then filter the "Missing Alt Text" column.

Sitebulb: Sitebulb's accessibility audit includes alt text checks alongside its technical SEO reports. It visualises issues at page level and site level, which makes it useful for prioritising. The free trial runs full audits; ongoing use requires a paid licence.

Both crawlers work best when you have already identified the scope of the problem and need a clean inventory to work from. Running them on a staging environment lets you verify fixes before going live.

For very large e-commerce catalogues — anything above 5,000 product pages — a crawler that respects robots.txt and rate-limits requests is important. Neither tool will get a site blocked if configured sensibly, but default settings can be aggressive.

What to do once you have found the gaps

Finding the issues is the quick part. Fixing them at scale requires a plan.

Start with traffic. Export your image audit alongside your analytics data, then sort by page visits. A missing alt on your top-selling product page is a higher priority than a missing alt in a rarely-visited archive post — for both accessibility compliance and organic search.

Product images come first for WCAG compliance. Under the European Accessibility Act, product images are functional: a screen reader user needs the alt text to understand what is being sold. Decorative banners and backgrounds can wait; product photography and any image that carries information cannot.

For meaningful alt text, the format that works on product pages is simple: [Product name], [key visual detail]. "Merino wool sweater, crew neck, in forest green" takes five seconds to write and meets WCAG 1.1.1 purpose requirements. For a catalogue of 500 products in multiple languages, that is where automated generation earns its place.

Set a baseline first. Recheck the same URL after fixes to confirm the error count drops. Screaming Frog and the online scanners both support recrawling, so running the same audit against a fixed page gives you a clear before-and-after number.

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Run a free WCAG scan on your storefront to see exactly where you stand — then start free to fix image alt text at scale.