Why image alt text is both an SEO and accessibility issue
Alt text serves two audiences: screen readers describing images to visually impaired users, and search engines understanding what each image depicts. Missing alt attributes fail accessibility audits (WCAG 2.1 Level A), get flagged by automated compliance tools, and remove a contextual ranking signal that Google uses for image search and AI Overviews.
Image search drives meaningful traffic. Google Images alone accounts for around 20% of all search queries. Every image without alt text is a missed chance to rank, both for image search and for the parent page's overall topical authority.
Decorative versus meaningful images
Not every image needs descriptive alt text. Decorative images (background patterns, divider lines, purely visual flourishes) should have empty alt attributes (alt=""). The empty attribute tells screen readers to skip the image entirely. Omitting the alt attribute completely is different and worse: screen readers read the file name aloud, which usually sounds like gibberish ("img- underscore-1234-dot-jpg").
For meaningful images, alt should describe what the image shows in the context of the page. A photo of a dog in a "dog breed guide" article should describe the dog and the breed. The same photo on a "pet adoption" page should focus on the adoption-relevant details.
Writing good alt text
Keep it under 125 characters. Screen readers cut off longer alt text. Be specific and contextual: "Golden retriever puppy chasing a tennis ball on grass" beats "Dog playing fetch". Avoid starting with "image of" or "picture of"; screen readers already announce that an image element exists.
Do not stuff keywords. Alt text full of target keywords reads unnaturally to screen readers and can trigger Google's keyword stuffing detection. Use the natural keyword if it describes what the image shows; do not force it.
For images of text (logos, infographics, screenshots with text), the alt should reproduce the text content of the image, not describe the image visually. "Quarterly revenue chart showing 23 percent growth" is better than "Bar chart with blue and gray bars".
What this checker actually looks for
Every img tag on the page. We extract the src and alt attributes for each, then categorize: missing alt entirely (worst), empty alt set explicitly (decorative, intentional), and alt with content. We report the first two as issues and provide the full list of all three for manual review.
We also flag suspiciously short alt text (under 5 characters that is not empty) and alt text that looks like a file name. Both usually indicate a CMS auto-filling alt with the image filename rather than someone writing real descriptions.
Common image alt mistakes
WordPress sites often have alt text auto-filled from the image filename. "DSC_4892.jpg" becomes alt="DSC 4892", which is useless. Configure your media library to require alt text on upload, or run a sweep updating alt fields for all existing images.
Lazy-loaded images sometimes appear without alt because the alt is set after page render via JavaScript. Search engines and accessibility tools may evaluate the page before that JavaScript runs. Use native loading="lazy" with alt set in the initial HTML rather than JS-injected.
Background images set via CSS do not have alt text at all. If the background image conveys important information, it should be a real img element with alt, not a CSS background. Background should be reserved for decorative imagery.
Image alt and AI search
AI search tools rely on alt text to understand image content, especially for queries that might surface images in answers ("what does X look like", "show me Y"). Pages with descriptive alt text more reliably surface their images in AI image cards and feature them in citations.
Alt text is also a natural signal for content quality. A page with 20 images, all with thoughtful alt text, signals to crawlers that this is a carefully edited piece of content. The same page with 20 missing-alt images signals templated or auto-generated content.