Alt Text Checker: 5 Ways to Find Missing Alt Text
Missing alt text is on every SEO audit. It's rarely fixed.
The backlog is the problem — not the intent. Most sites don't know which images are missing it or how many.
Two things break when alt text is absent. Search crawlers can't index the image's content — the <img> tag exists, but there's nothing to read. Screen readers announce the filename or the word "image" instead of a description, which is useless to someone who can't see the page.
Key Takeaways
- A missing
altattribute and an emptyalt=""are different problems — treating them the same breaks your audit- DevTools and Lighthouse work for single-page checks; Screaming Frog and FastAltText handle site-wide audits
- FastAltText is the only method here that audits and fixes in the same workflow, with automatic decorative image classification
- Prioritize content-bearing images first — product shots, charts, hero images carry the most SEO and accessibility weight
Missing Alt Text vs. Empty Alt Text — Know the Difference
Two different problems. A missing alt attribute is an error — screen readers announce the filename. An empty one (alt="") is intentional: skip the image entirely and it's valid for dividers, background icons, and visual flourishes that add nothing to the page.
At scale, the distinction matters. Fix a decorative image with a description and you've added noise. Leave a content image blank and Google can't index your images and users who rely on screen readers can't navigate them. Per WCAG guidelines, decorative images must have alt="" — omitting the attribute entirely is a failure, not a neutral state.
FastAltText Bulk Updater classifies them automatically so you don't make that call 400 times.
Five Ways to Find Missing Alt Text
The right method depends on how many pages you're dealing with.
Browser DevTools
The fastest way to check a single page. Right-click any image → Inspect. In the Elements panel:
- Hit Ctrl+F and search for
img - Look for tags without an
altattribute - Or with
alt=""where there shouldn't be one
No install. No account. Done in under two minutes.
The limit is obvious: one page at a time. Fine for a spot check, not for a site with 200 pages.
While you're in there, check what the existing alt text actually says. Filenames used as alt text (DSC_0042.jpg) and auto-generated strings (image001) are technically present but functionally useless — they show up as "filled" in Screaming Frog and most SEO crawlers but still need rewriting.
Google Lighthouse
Already in your browser if you use Chrome. Open DevTools → Lighthouse tab → run an Accessibility audit.
Lighthouse flags every image missing an alt attribute and lists them by element. It's plain-language output — no configuration needed.
Same limit as DevTools: one page per run. Useful for a quick accessibility pass, not a site-wide inventory.
It also catches related issues in the same run — missing form labels, low contrast text, missing ARIA attributes. If you're preparing for an accessibility audit, it's worth running on your highest-traffic pages before reaching for a crawler.
Screaming Frog
The standard tool for site-wide image audits. Crawl your site, open the Images tab, and filter by "Missing Alt Text." Every offending image surfaces with its source URL.
Export to CSV: you get the full list — page URL, image src, current alt text — ready to work from.
Free tier covers up to 500 URLs. For larger sites, Semrush, Ahrefs, and Sitebulb flag the same data in their site audit modules.
The gap: it finds the problem. It doesn't fix it. You still need a separate workflow for remediation.
Run the same filter for "Alt Text" with no missing flag too — this surfaces images where alt text exists but contains a filename or templated string. It's a separate problem the missing-only filter won't catch.
FastAltText Bulk Checker
Submit your sitemap URL or paste a list of pages. FastAltText crawls every one, identifies every image with missing alt text, and classifies each as decorative or content-bearing.
The difference from every other method here: the audit and the fix are the same workflow. Review flagged images, generate alt text, export CSV or push directly to WordPress or Shopify. For a full comparison of available tools, see alt text generators compared.
No switching tools. No orphaned spreadsheet.
The free tier covers 20 images per day — enough to audit and fix a small site or a single client page in one session. For larger backlogs, paid plans handle bulk generation across the full site in one pass.
Dedicated Online Checkers
Tools like SEOptimer, Scribely, and Sitechecker are free alt text checkers that accept a single URL and return a report in seconds. No account required, no install.
Useful for a quick sanity check on a specific page. Not practical for anything site-wide.
Where they earn their place: checking a page before it goes live, or verifying a fix without opening a full crawler. If a client asks whether a specific landing page has alt text issues, this is faster than spinning up Screaming Frog for one URL.
What to Do Once You've Found Them
Not every image needs the same fix. Content-bearing images — product shots, charts, diagrams, hero images — need accurate descriptions. Decorative images need alt="" and nothing else. Start with the ones that carry SEO and accessibility weight.
Prioritize by impact, not volume. A product image on a high-traffic category page matters more than a stock photo buried in a blog post from 2019. For the mechanics of how AI generates those descriptions, see how AI alt text generators actually work.
FAQ
How do I know if an image has alt text?
Right-click the image → Inspect. Look for the alt attribute in the <img> tag. Empty quotes (alt="") means decorative — intentional. No alt attribute at all means it's missing.
Do you need alt text for decorative images?
No description, but yes attribute. Decorative images need alt="" so screen readers skip them. Leaving the attribute out entirely is still an error.
How do I check if a site has alt text across all pages?
Use a site crawler like Screaming Frog, or a bulk checker like FastAltText that accepts a sitemap or URL list. Single-page tools won't scale.
Is alt text searchable?
By search engines, yes. Google uses alt text to understand and index image content. It's not visible to users browsing your site.
Conclusion
The audit is the easy part. Every method in this article surfaces missing alt text in minutes. What keeps a site fixed is a clear workflow: classify first, prioritize by impact, and use a tool that can handle the volume.
For fewer than 20 images, DevTools and manual writing is fine. For anything larger, you need a bulk approach — not because the individual task is hard, but because doing it 400 times is exactly the kind of work that never gets done.
Start with the audit. Fix what matters most.