HTML Alt Text Checker: Find Missing Image Alt Text in Seconds
Learn how the HTML Alt Text Checker scans your markup for missing alt attributes, empty alt text, and broken img tags — and how to write alt text that passes WCAG 1.1.1.
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Every image on your page sends a message. To a sighted visitor, it's the picture itself. To a screen reader user, it's whatever you put in the alt attribute — and if you left that attribute out, the message is silence. Missing alt text is one of the most common accessibility failures on the web, and it's also one of the easiest to fix once you know where it hides.
That's exactly what the HTML Alt Text Checker does. Paste your markup, hit scan, and get a structured report showing every <img> element that's missing alt text, has an empty alt, or has a broken src attribute — complete with line numbers, column positions, and severity levels. No signup, no upload, everything runs locally in your browser.
Whether you're preparing for a WCAG audit, cleaning up after a CMS migration, or just doing a final pass before a release, this guide shows you how to use the checker effectively and how to write alt text that genuinely helps your users.
Why Use the HTML Alt Text Checker?
- Screen reader accessibility. Assistive technology announces the alt attribute when it encounters an image. No alt means no information — the user literally skips past your hero banner, product photo, or chart without knowing it existed.
- WCAG 1.1.1 compliance. The Web Content Accessibility Guidelines require text alternatives for all non-text content at Level A — the baseline every site should meet. Regulators and enterprise clients increasingly check for it.
- SEO that costs nothing extra. Search engines can't "see" your images either. Alt text is how you tell them what's in the picture, and it's what browsers display when an image fails to load.
- Line-precision reporting. The checker doesn't just say "3 problems found." It tells you the exact line and column of every issue, so you can jump straight to the offending tag instead of hunting through a 400-line template.
- Catches more than missing alt. Empty alt attributes that may not be intentional, images with no src, and malformed <img> tags all show up in the same report — the bugs that usually slip through a visual review.
- Zero-friction workflow. The tool runs entirely client-side. Your HTML never leaves the browser, which matters when you're auditing proprietary templates, client work, or internal dashboards.
Key Features
| Check | Severity | What it means |
|---|---|---|
| Missing alt attribute | Error | Image has no alt at all — screen readers get nothing |
| Empty alt with src present | Warning | Often intentional for decorative images, but worth reviewing |
| Missing src attribute | Error | Image tag renders nothing — likely a build or CMS failure |
| Broken / incomplete <img> tag | Error | Malformed markup the browser can't parse correctly |
| Image with proper alt text | Pass | Alt is present and non-empty — confirm the wording is meaningful |
- Severity-coded results. Errors, warnings, and passes are color-coded in the report, with a summary panel showing total images, error count, warning count, and passes at a glance.
- Exportable report. One click copies or downloads a formatted "Accessibility Report — Image Alt Text" as a .txt file — perfect for attaching to a ticket, sending to a client, or keeping as an audit record.
- Sample loader. Not sure what to scan first? The Load Sample button drops in example HTML so you can see how each issue type appears in the report before running it against your own code.
How to Use
- Open the HTML Alt Text Checker — there's nothing to install or configure.
- Paste your HTML into the input area, or click Load Sample to explore with example markup.
- Click Scan (or the equivalent check button) to run the analysis.
- Review the report: each issue card shows its severity, the problem, and the exact line and column. The summary stats tell you how much work you have.
- Fix the flagged tags in your source, re-scan, and when you're done use Copy Report or Download to export the results for your records or your team.
Understanding Alt Text and WCAG 1.1.1
WCAG success criterion 1.1.1 (Non-text Content) requires a text alternative for every image that conveys information. The nuance most people miss is that "text alternative" doesn't always mean "visible caption" — it means the alt attribute serves as the programmatic text.
Missing alt vs. empty alt. These are very different failures. A missing alt attribute is an error: screen readers may fall back to announcing the filename ("underscore hero underscore final two dot jpg"), which is noise. An empty alt (alt="") tells assistive technology to skip the image entirely — which is the correct choice for purely decorative images like spacer graphics, background flourishes, or ornamental dividers.
Because empty alt can be either intentional design or a lazy mistake, the checker flags it as a warning rather than an error. When you see one, ask: does this image communicate anything? If yes, write real alt text. If it's genuinely decorative, the empty alt is correct and you can move on.
What good alt text sounds like. A screen reader reads your alt verbatim, so write it as if you were describing the image to someone on the phone, in one concise sentence. alt="chart" is technically present but nearly useless; alt="Bar chart: revenue grew 40% from Q1 to Q4 2025" carries the actual information. For functional images — a logo that links home, an icon button — describe the action, not the picture: alt="Home" on a logo link, not alt="Company logo image".
Why line and column numbers matter. In a real codebase, the same broken pattern gets copy-pasted across templates. Knowing that the error sits at line 12, column 8 lets you fix the source template rather than chasing each rendered page. The checker's report mirrors how linters report issues, so the fix workflow feels familiar to any developer.
Practical Use Cases
Pre-release template audits
Before shipping a new landing page or email template, paste the final HTML into the checker. It takes seconds and catches the images that were added late in the design process — the ones most likely to have been dropped in without alt text. Fix errors, review warnings, export the report as your release artifact.
Post-migration cleanup
CMS migrations are notorious for stripping attributes. Moving from one platform to another, or converting Markdown to HTML, often produces <img> tags that lost their alt along the way. Scanning the migrated output gives you a precise punch list instead of a vague sense that "some images look off."
Agency and freelance client work
If you deliver accessibility fixes to clients, an exported report before and after your work is tangible evidence of value delivered. The severity breakdown and line references make it easy to scope the job and to show exactly what changed.
HTML email and newsletters
Email clients are the wild west of rendering — images blocked by default in many clients means alt text is often the only thing recipients see. Run your newsletter HTML through the checker before every send; the missing-src check also catches images whose paths broke during templating.
Best Practices for Writing Alt Text
- Describe the information, not the image. Focus on what the image communicates in context, not its visual appearance. A photo of a team matters as "our support team at the 2026 offsite" — details of clothing rarely add meaning.
- Keep it to one concise sentence. Screen readers read the whole thing aloud with no pause. If you need three sentences, that content probably belongs in a caption or body text.
- Never start with "image of" or "picture of." The screen reader already announces it as an image. Redundancy slows users down.
- Use empty alt deliberately for decoration. alt="" is the correct pattern for spacers, dividers, and background flourishes. The checker's warning is your cue to confirm intent, not an automatic defect.
- Describe actions for functional images. Icons in buttons and linked logos should describe what happens — "Search," "Home," "Download PDF" — not what the icon looks like.
- Include key text from text-as-image. If your graphic contains text (a chart label, a quote card), that text belongs in the alt attribute, because it's the only version screen reader users get.
Start Checking Your Alt Text Today
Alt text is the rare accessibility fix that improves three things at once: screen reader experience, SEO, and image-fail fallbacks. And unlike most compliance work, verifying it takes seconds. Paste your most important page's HTML into the HTML Alt Text Checker, scan it, and fix what comes back. Your users — and your search rankings — will notice.
Related Tools You Might Like:
- ARIA Label Checker — verify ARIA labels on interactive elements
- Accessible Name Calculator — see the exact accessible name assistive tech computes
- Unused CSS Finder — trim dead styles from your stylesheets
Happy auditing!