What is Alt-Text? Complete Guide to Writing Accessible Image Descriptions for SEO and Inclusion

What is Alt-Text?

Alt-text (alternative text) is a written description of an image that serves as a text replacement when images cannot be displayed or accessed. Originally designed for users with visual impairments who rely on screen readers, alt-text has become essential for web accessibility, SEO optimization, and ensuring content remains functional across all devices and connection speeds. Alt-text appears in the HTML img tag as the "alt" attribute and should concisely describe the image's content and purpose.

Effective alt-text serves dual purposes: it makes content accessible to all users while providing search engines with context about visual content, improving both user experience and discoverability.

Why Alt-Text is Critical for Digital Content Success

• Web Accessibility: Ensures content is usable by people with visual impairments and assistive technologies
• SEO Benefits: Helps search engines understand and index visual content for improved rankings
• Legal Compliance: Required for ADA compliance and avoiding accessibility-related legal issues
• User Experience: Provides context when images fail to load due to slow connections or technical issues
• Content Comprehension: Enhances understanding for users who process text better than visual information

Key Benefits of Strategic Alt-Text Implementation

Enhanced Website Accessibility

Proper alt-text makes visual content accessible to the 285 million people worldwide with visual impairments, ensuring equal access to information and improving user experience for assistive technology users, while also benefiting users with cognitive differences or processing preferences.

Improved Search Engine Optimization

Search engines rely on alt-text to understand image content, improving image search rankings and overall page SEO. Well-written alt-text can drive significant traffic through image search results and helps search engines better understand page context and relevance.

Better Content Resilience

Alt-text ensures your content remains meaningful and functional even when images don't load properly due to slow connections, technical issues, or different browsing environments, maintaining communication effectiveness across all scenarios.

Essential Alt-Text Types and Content Applications

• Descriptive Alt-Text: Objective descriptions of image content for photographs, illustrations, and graphics
• Functional Alt-Text: Descriptions focusing on image purpose and function for buttons, links, and interactive elements
• Decorative Alt-Text: Empty alt attributes (alt="") for purely decorative images that don't add content value
• Complex Alt-Text: Brief descriptions with links to longer descriptions for charts, graphs, and detailed visuals
• Context-Dependent Alt-Text: Descriptions that vary based on surrounding content and image purpose

The Accessibility Science Behind Effective Alt-Text

Alt-text works by providing screen readers and other assistive technologies with textual information that can be converted to speech, braille, or other accessible formats. The goal is to convey the same essential information that visual users receive from images, ensuring equivalent user experiences across different abilities and technologies.

Understanding how assistive technologies process alt-text helps create descriptions that are not only accurate but also useful and efficient for users who depend on these tools for web navigation and content consumption.

How to Write Effective Alt-Text: Complete Writing Framework

Step 1: Analyze Image Purpose and Context

• Determine whether the image is decorative, informative, functional, or complex
• Consider the image's role within the surrounding content and overall page purpose
• Identify the key information or message the image conveys to visual users
• Assess whether the image requires a brief description or more detailed explanation
• Consider your audience's needs and the context in which they'll encounter the image

Step 2: Write Clear, Concise Descriptions

• Keep descriptions under 150 characters when possible for optimal screen reader performance
• Start with the most important information and work toward supporting details
• Use specific, concrete language rather than vague or subjective descriptions
• Avoid redundant phrases like "image of" or "picture showing" unless necessary for clarity
• Include relevant details about people, objects, settings, and actions shown in the image

Step 3: Optimize for Both Accessibility and SEO

• Include relevant keywords naturally when they accurately describe image content
• Balance SEO optimization with accessibility needs, prioritizing user experience
• Use industry-standard terminology and language that your audience understands
• Ensure alt-text makes sense when read aloud by screen readers
• Avoid keyword stuffing or descriptions that don't accurately reflect image content

Step 4: Test and Refine Alt-Text Effectiveness

• Use screen reader software to test how your alt-text sounds when read aloud
• Have users with visual impairments review your alt-text for clarity and usefulness
• Monitor image search performance and traffic to assess SEO effectiveness
• Conduct accessibility audits to identify and improve alt-text quality
• Update alt-text when images are updated or when context changes significantly

Alt-Text Best Practices for Accessibility and SEO Success

• Be Specific and Accurate: Describe exactly what's in the image rather than interpreting or adding assumptions
• Consider Context: Write descriptions that make sense within the surrounding content and page purpose
• Keep It Concise: Provide essential information efficiently without unnecessary detail
• Use Natural Language: Write in clear, conversational language that flows naturally when read aloud
• Include Relevant Keywords: Incorporate SEO keywords only when they accurately describe the image content

Alt-Text FAQ: Accessibility and SEO Implementation Questions

When should I use empty alt-text (alt="") versus descriptive alt-text?

Use empty alt-text for purely decorative images that don't add informational value, like background patterns or design elements. Use descriptive alt-text for images that convey information, show products, illustrate concepts, or serve functional purposes. When in doubt, consider whether removing the image would affect content understanding.

How do I write alt-text for complex images like charts or infographics?

For complex images, use brief alt-text that identifies the image type and main topic, then provide a longer description elsewhere on the page or via a link. For example: alt="Sales growth chart showing 40% increase over 3 years" with detailed data provided in accompanying text or a data table.

Should alt-text be different for the same image used in different contexts?

Yes, alt-text should reflect the image's purpose in each specific context. The same product photo might be described as "Blue running shoes" on a category page but "Blue running shoes, size 9, $120" on a product detail page, focusing on the information most relevant to each page's purpose.

How do I balance SEO keywords with accessibility in alt-text?

Accessibility should always be the priority. Include keywords only when they naturally and accurately describe the image content. Keyword stuffing makes alt-text less useful for screen reader users and can harm SEO. Focus on clear, accurate descriptions that happen to include relevant search terms.

What are common alt-text mistakes that hurt both accessibility and SEO?

Common mistakes include using generic descriptions like "image" or "photo," writing overly long descriptions that overwhelm screen reader users, keyword stuffing that creates unnatural language, describing obvious elements while missing important details, and using the same alt-text for different images.