Image alt text linter: audit HTML for accessibility + SEO.
Image alt text is required by WCAG 2.2 (Section 1.1.1 Non-Text Content) and Section 508 for federal accessibility compliance. It is also a major source of Google Image search impressions — proper alt text increases image search visibility by 30 to 70 percent in 2026 testing. This linter audits HTML for the most common alt text failures.
About this tool.
Alt text serves three functions: accessibility (screen readers read it to blind and low-vision users), SEO (Google Image search reads it to understand image content), and graceful degradation (text appears if the image fails to load). Missing alt text fails WCAG 2.2 Section 1.1.1 and Section 508. Empty alt text on non-decorative images is the same failure.
Optimal alt text is 50 to 125 characters, describes the image content meaningfully, does not start with redundant phrases like 'image of' or 'picture of' (screen readers already announce the element as an image), and uses natural language rather than keyword stuffing. Length over 125 characters is excessive and gets truncated by some screen readers.
Decorative images that add no informational content should have empty alt text plus role=presentation. The combination tells screen readers to skip the image entirely. Common decorative cases: visual separators, background flourishes, icons next to text that already conveys the meaning.
Google Image search reads alt text as a primary signal. Research from 2025 to 2026 found pages with descriptive 50 to 125 character alt text achieved 30 to 70 percent more Google Image search impressions than pages with missing or empty alt text. Image search is approximately 22 percent of all Google searches — a massive impression channel.
The most common failure modes this linter catches: completely missing alt attribute, empty alt without role=presentation, alt text starting with 'image of' or 'photo of' (redundant), excessively short alt text under 5 characters (likely not descriptive), excessively long alt text over 250 characters (likely keyword-stuffed).
ThatDeveloperGuy applies alt text auditing to every site we build via axe-core in CI plus manual review with NVDA, JAWS, and VoiceOver. We deliver a VPAT documenting alt text conformance as part of every federal-grade engagement. See /services/section-508-compliance/ for the full methodology.
FAQ.
What's the maximum alt text length?
WCAG has no hard limit, but practitioner consensus is 125 characters for screen reader readability. Beyond that, some screen readers truncate. For SEO, 50-125 characters is the sweet spot.
How do I handle decorative images?
Set alt='' (empty) plus role='presentation'. The combination tells screen readers to skip the image entirely. Without role='presentation', empty alt is ambiguous.
Should I include keywords in alt text?
Naturally, yes — alt text is a Google Image search ranking signal. But never stuff. The best alt text reads like a natural description that happens to include relevant terms.
What about decorative SVGs?
SVG with aria-hidden='true' is the cleanest pattern for decorative icons. For meaningful SVGs, use role='img' plus aria-label.
How does this affect ADA Title III lawsuits?
Missing alt text is one of the most-cited accessibility failures in ADA Title III lawsuits. Serial-litigant plaintiffs run automated scans of small business sites looking for it. Adding proper alt text site-wide is one of the cheapest legal-risk mitigations available.
Can I auto-generate alt text with AI?
GPT-4 Vision and Claude Vision can generate decent alt text. Always human-review the output — AI sometimes hallucinates details that aren't actually in the image, which can be embarrassing or legally problematic.
Built by Joseph W. Anady at ThatDeveloperGuy. Need professional help? Get a free 48-hour audit.