What Is an Alt Attribute?
The alt attribute (short for "alternative text") is an HTML attribute applied to image tags that provides a text description of the image's content. In the HTML source of a page, it appears as <img src="product-photo.jpg" alt="Blue noise-cancelling headphones on white background">. This text serves two distinct purposes: it is read aloud by screen readers for visually impaired users, and it is parsed by search engine crawlers to understand what an image depicts.
Search engine crawlers cannot "see" images in the way humans do. Without alt text, a crawler must infer image content from surrounding text, file name, and contextual signals — a far less reliable process than direct description. Well-written alt text removes this ambiguity, allowing the crawler to accurately categorize the image for both web search and image search indexing.
Alt attributes should be descriptive and specific. Poor alt text ("image1.jpg" or simply "photo") provides no useful information. Overstuffed alt text that packs in keywords without describing the actual image is a spam signal. Good alt text describes what is in the image clearly and concisely — the same description you would give to someone who cannot see the image. If the image contains text (a chart title, a call-to-action button), that text should appear in the alt attribute.
Why Alt Attributes Matter for Marketers
Alt text optimization is one of the highest-value, lowest-effort technical SEO improvements available. On content-heavy sites — blogs, e-commerce stores, news publications — images are ubiquitous, and every missing or poorly written alt attribute represents a crawling and indexing opportunity that is being wasted.
The accessibility argument is equally important. The Americans with Disabilities Act (ADA) and the Web Content Accessibility Guidelines (WCAG) establish standards that require web content to be accessible to users with disabilities. Missing alt text on meaningful images is a WCAG violation and can expose organizations to ADA compliance risk, particularly for larger commercial websites. Beyond legal compliance, accessible content reaches a broader audience and improves user experience for all visitors, including those using slow connections where images may not load.
For e-commerce sites specifically, image search is a meaningful acquisition channel — particularly for visually-driven product categories like apparel, furniture, and food. Products with descriptive, keyword-relevant alt text are more likely to appear in Google Images results, driving incremental traffic that never comes from text-based search alone.
How to Implement Alt Attributes
Audit all images on your site using a crawl tool (Screaming Frog, Sitebulb, or Ahrefs' site audit) to identify images with missing or duplicate alt text. Prioritize high-traffic pages and pages where images are central to the content.
Write alt text that describes the image accurately. For product images: include the product name, key color or variant, and context ("black leather laptop bag with shoulder strap"). For illustrative blog images: describe what is depicted and why it is relevant to the surrounding content. For decorative images that serve no informational purpose (dividers, backgrounds), use an empty alt attribute (alt="") to signal to screen readers that the image can be safely skipped.
Integrate alt text writing into your content production workflow. Writers should draft alt text for every image they select before submitting for publication, rather than treating it as an afterthought during technical review.
How to Measure Alt Attribute Performance
Track image search impressions and clicks in Google Search Console's "Search type: Image" filter. Growth in image search traffic following an alt text optimization campaign confirms that improved alt attributes are improving image indexing.
Monitor the percentage of images with missing alt text in regular site crawls. Targeting 100% coverage is realistic for most sites; track progress toward this goal quarterly.
Alt Attributes and AI Search
AI systems that process web content for knowledge and citation purposes increasingly work with multimodal content — text and images together. Well-written alt text ensures that the information conveyed by images is accessible to AI systems parsing your pages, not just to human readers. For infographics, data visualizations, and charts that contain key statistics or frameworks, alt text (and supplementary caption or figure description text) ensures the data is machine-readable. This is particularly relevant for AI systems that may incorporate factual claims from images into generated answers — proper alt text increases the probability that your visual content contributes to AI citations, not just your text content.