Alt text

Millions of people use screen readers to browse the web. For them, an image without alt text is invisible. A picture of your product, a chart showing data, a screenshot demonstrating a workflow, all of it disappears if you skip alt text. This is not just an accessibility issue; it is a content and SEO problem.

Google cannot see images the way humans do. It relies on context clues: the image filename, surrounding text, and alt text. Of these, alt text is the clearest signal of what an image shows. Without it, Google may misinterpret or skip your images entirely, leaving traffic on the table in image search and losing a ranking signal for your page.

What alt text really is and why it matters

Alt text is an HTML attribute (alt="...") that contains a short text description of an image. It serves two purposes: it allows screen readers to describe images to blind and low-vision users, and it tells search engines what an image contains so they can index it for image search and visual understanding.

Unlike captions, which appear on the page, alt text is invisible to sighted users. It exists purely in the HTML. This means you can optimize it for search and accessibility without affecting visual design.

Google has confirmed that alt text is not a direct ranking factor for page search. However, it is a ranking factor for image search. Plus, better image understanding helps Google grasp the topic of your page. If your article on on-page SEO includes a screenshot of a well-optimized page and that screenshot has descriptive alt text, Google better understands your article is authoritative on the topic.

How to write effective alt text

Describe what you see, not the fact that it is an image. Never start alt text with "image of" or "screenshot of." Just describe the content. A photo of a laptop showing a Google search results page with the words "Sorank SEO Tool" visible should be: "Google search results showing Sorank SEO tool in the top three rankings."

Be specific and concise. Vague alt text like "chart" or "graph" wastes the opportunity. Better: "Bar chart comparing organic traffic growth over 12 months for Sorank versus Ahrefs."

Include relevant keywords when they fit naturally. If your image is a screenshot of the Sorank dashboard, alt text like "Sorank dashboard showing keyword research metrics and ranking data" works. Do not force keywords that have nothing to do with the image.

Keep it short. Aim for 125 characters or fewer, usually one sentence. Screen readers process alt text sequentially, and long descriptions slow down navigation. If you need more context, add a caption below the image or a paragraph of body text.

For decorative images that add no informational value, use empty alt text: alt="". This tells screen readers to skip the image. Do not omit the alt attribute entirely; use alt="" explicitly.

Common alt text mistakes

Keyword stuffing is rampant. Alt text like "best SEO tools, keyword research tools, backlink checker, competitive analysis" is unreadable and violates accessibility guidelines. Google may penalize it as spam. Write for humans first.

Missing alt text on important images is equally bad. Many sites add images and never fill in the alt attribute. This loses accessibility credibility and image search traffic. Audit your site regularly for missing alt attributes.

Repeating the surrounding text is wasteful. If your heading already says "SEO Tools Comparison Chart," your alt text should add information, not repeat it. Try "Comparison chart showing Sorank, Ahrefs, and Semrush pricing and features."

Using filename as alt text is lazy. Do not rely on "image_2024_11_15.jpg" or "unnamed_1.png." These convey nothing. Always write a real description.

Alt text and image search optimization

Image search is a growing channel. Users search for images of products, tutorials, infographics, and tools daily. Your image will only appear in image search if Google understands it. Image alt text is one of the strongest signals for this.

Make sure your alt text includes relevant terms searchers might use. If your image is a screenshot of schema markup on a page, searchers might type "schema markup example" or "JSON-LD code screenshot." Include these variants in alt text when appropriate.

Also optimize your image filename and the caption below the image. Together, alt text, filename, and caption help Google understand the full context.

Alt text for charts, graphs, and data visualizations

Data visualizations need special care. A generic alt text like "graph" helps nobody. Describe the key data. Example: "Line graph showing organic traffic rising from 5,000 to 25,000 monthly sessions over six months after implementing technical SEO improvements."

For complex infographics, you may need more than alt text alone. Consider adding a detailed text explanation in the surrounding content, or a downloadable text version of the data.

Measuring alt text impact

Check Google Search Console under the Images section. Look for which images are driving impressions and clicks from image search. If important images are missing from image search, they likely lack descriptive alt text or relevant surrounding content.

Monitor accessibility. Tools like Google Lighthouse and WAVE screen reader checkers flag missing alt text. Aim for 100 percent compliance; it signals quality to both users and Google.

Conclusion

Alt text is foundational to accessible, indexable content. Write every alt attribute as if a screen reader user and a search engine bot will read it. Be specific, include keywords when natural, stay under 125 characters, and never skip this step. The effort is minimal, but the impact for accessibility and image search is substantial. When managing hundreds of images, tools help you audit and bulk-add alt text where it is missing. Our SEO audit tool identifies all images lacking alt text so you can fix them systematically.