Writing effective alt text: Key principles, roles, and SEO benefits

Alternative text (alt text) is a small detail with a big impact. It provides a written description of an image that screen readers vocalize, helping users who are blind or visually impaired understand visual content. It also assists search engines in comprehending your images, boosting SEO.

Three considerations when writing alt text

1. Understand the image’s purpose
   Ask, “Why is this image here?” The image’s role—whether decorative, informative, functional, or complex—guides how (or if) alt text should be written.
2. Describe what’s essential
   Focus on the key elements users need to understand. Be specific and concise (typically under 125 characters) and avoid starting with “Image of…” or “Picture of…” since screen readers already announce that it's an image.
3. Consider the context
   Tailor your alt text to the surrounding content. If the image reinforces nearby information, a brief description may suffice; if it introduces new information, provide a more detailed description or link to a longer explanation elsewhere.

Assessing the image’s role

When writing alt text, consider the image’s role on the page:

• Functional: If the image serves as a link or button, the alt text should describe its function or destination.
• Decorative: If the image is solely for visual appeal, use an empty alt attribute (alt="") so that screen readers can skip it.
• Informative: If the image conveys essential information not found in the text, succinctly describe its content to aid comprehension.
• Complex: For images that present multiple points (such as charts, diagrams, or infographics), include a brief summary in the alt text and provide a more detailed description in the surrounding content or a caption.

Best practices for alt text and SEO

• Keep it concise: Aim for under 125 characters.
• Skip “image” or “photo”: These terms are redundant.
• End with a period: This prompts a natural pause for screen readers.
• Front-load key information: Place the most important details at the beginning.
• Avoid jargon and unclear abbreviations: Use simple, familiar language.
• Tailor to context: Customize alt text based on the image’s specific role on each page.
• Always include the alt attribute: Even if empty, include (alt="") to prevent screen readers from announcing the file name.

Screen readers rely on descriptive, keyword-relevant alt text to understand your images, which can enhance image search visibility, page relevance, and overall accessibility—ultimately contributing to improved SEO. Pro tip: Use relevant keywords naturally; avoid stuffing or over-optimizing.

If you’d like to learn more about why alt text matters, here are a few helpful resources to explore:

• Alt text as one of the 7 core skills – Office for Digital Accessibility
• Accessibility Ambassadors December session: Hands-on practice with alternative text
• Accessibility training options
• W3C tips and tricks

In upcoming posts, we’ll dive deeper into the four image roles by exploring different image types, their context, and examples of effective alt text—starting with functional images. If others on your team don’t receive the Communications Blog, they can subscribe to stay updated on the series.

If you have additional questions about alt text, reach out to the University Marketing Communications Digital Communications Team at [email protected].