Image Alt Text: Why It Is Important and How to Write It

The alt attribute on an <img> tag provides a text alternative for the image. Browsers display the alt text when the image fails to load. Screen readers speak the alt text aloud for blind and low-vision users. Search engine crawlers read the alt text to understand what the image depicts, since they cannot process visual content the way humans do.

Why Alt Text Matters for SEO

Google Images drives a significant share of web traffic across many niches, particularly in e-commerce, recipes, travel, and interior design. Pages with descriptive, keyword-relevant alt text rank in image search results, bringing additional traffic beyond standard web search.

Beyond image search, Google uses alt text as a contextual signal when evaluating page relevance. An article about "home office desk setups" that contains images with alt text describing specific desk configurations reinforces the topical relevance of the entire page. This helps Google confirm that the content delivers what the title and headings promise.

The Anatomy of Effective Alt Text

Good alt text describes what the image shows in plain, specific language. Imagine describing the image to someone on a phone call who cannot see a screen. That description, concise and factual, forms the basis of good alt text.

For a product image of white running shoes on a white background: alt="BRAND MODEL X running shoes in white, side view". For an infographic showing website traffic growth: alt="Bar chart showing 140 percent year-over-year website traffic growth from 2024 to 2025". Both descriptions tell Google and screen reader users exactly what they would see.

Length and Specificity

Keep alt text under 125 characters. Screen readers typically truncate longer descriptions, and Google places less weight on alt text that reads like keyword stuffing. A precise description in fewer words outperforms a verbose one padded with extra keywords.

Include the primary keyword naturally where it genuinely describes the image. If your page targets "standing desk ergonomics" and the image shows a person standing at a desk with a monitor at eye level, an alt text of "ergonomic standing desk setup with monitor at eye level" serves both purposes without forcing the keyword awkwardly.

When to Leave Alt Text Empty

Decorative images that add no informational value should carry an empty alt attribute: alt="". This tells screen readers to skip the image entirely, avoiding a disruptive "image" announcement in the middle of a flowing text read. Examples of decorative images include background textures, divider lines, and purely aesthetic icon patterns that appear alongside labelled text.

Do not omit the alt attribute entirely. A missing alt attribute forces screen readers to announce the image filename, which typically looks like IMG_4829.jpg and provides no useful information.

Alt Text for Different Image Types

Product Images

Include the product name, key distinguishing attributes (colour, size, material), and perspective (front view, side view, lifestyle shot). For e-commerce sites with hundreds of product variants, templated alt text structures with dynamic variables work well: alt="{Product Name} in {Colour}, {Perspective}".

Charts and Infographics

Describe what the data shows, not just the chart type. "Pie chart of marketing channel distribution" tells the reader nothing useful. "Pie chart showing organic search drives 52 percent of total traffic, paid search 28 percent, and social 20 percent" gives them the actual insight the chart communicates.

People and Settings

Describe the action or context rather than physical appearance. "Developer reviewing code on dual monitor setup in a home office" serves the user and the search engine better than "person at a computer" or, worse, physical descriptions of the individual.

Icons

Icons paired with visible text labels should carry empty alt attributes because the adjacent text already communicates the meaning. An icon next to a button labelled "Download Report" does not need alt text that repeats the label.

File Names Complement Alt Text

Google reads image file names as an additional signal alongside alt text. Rename images before uploading them. standing-desk-ergonomic-setup.jpg reinforces the same topical signal as the alt text. IMG_4829.jpg adds no context whatsoever. Together, a descriptive file name and accurate alt text create a consistent signal that strengthens image search visibility.

Alt Text and the title Attribute: Two Different Jobs

Many site owners confuse the alt attribute with the title attribute on images. The title attribute generates a small tooltip when a user hovers a mouse over the image, a behaviour that means nothing on touch devices and provides almost no SEO value on its own. The alt attribute serves accessibility and search purposes simultaneously and matters far more for both. Write meaningful alt text on every content image first, and add a title attribute only when a hover tooltip genuinely helps the user, such as labelling an interactive icon.

Captions Strengthen the Same Signal

A visible image caption sitting directly beneath an image gives both users and Google additional context about what the image shows. Captions tend to receive disproportionate reading attention because they sit at a natural pause point in the page layout, which makes them a strong place to reinforce the page's primary topic in natural language. Use captions for images where extra explanation helps the reader, and let the alt text remain a concise standalone description for accessibility purposes.

Auditing Alt Text at Scale

Large sites often have thousands of images, many uploaded without alt text. Crawl your site with an SEO tool that flags missing alt attributes, empty alt text on non decorative images, and suspiciously long alt text that may indicate keyword stuffing. Prioritise fixing alt text on product images and blog post featured images first, as these carry the highest commercial and informational value.

Build alt text writing into your content workflow rather than treating it as a cleanup task. Require writers and content editors to add descriptive alt text at the moment they upload an image, since retrofitting alt text across an existing library of thousands of images takes far longer than writing it correctly the first time.