Alt Text

How alternative text descriptions improve SEO performance, accessibility, and image search visibility

What Is Alt Text?

Alt text (alternative text) is a written description of an image that appears in your website's HTML code. It serves two essential functions: helping search engines understand what images show and providing descriptions for users who cannot see them. When you add an image to a webpage, the description goes into the HTML "alt" attribute within the image tag.

If an image fails to load or a user hovers over it, the description appears on screen. For visually impaired visitors using screen readers, the text is read aloud, making your visual content accessible to everyone. Search engines also read these descriptions to understand your images and rank them in image search results.

Simple explanation: Alt text is a brief description added to images that helps both search engines and people understand what the image shows. Well-written descriptions improve your SEO whilst making your website accessible to all users.

Why Alt Text Matters for SEO

Image descriptions are a crucial on-page SEO element. Search engines cannot "see" images the way humans do—they depend entirely on textual descriptions to understand visual content. Well-optimised descriptions help search engines in several important ways:

• Content understanding: Clear descriptions tell Google exactly what each image depicts
• Image search rankings: Properly described images rank higher in Google Images
• Keyword relevance: Natural keyword inclusion strengthens page relevance for target queries
• Overall page quality: Every optimised element contributes to better rankings
• Contextual signals: Descriptions help search engines understand how images relate to surrounding content

How to Write Effective Alt Text

Great image descriptions are descriptive, concise, and relevant to your content. Follow these best practices when writing descriptions that improve both SEO and accessibility:

• Be descriptive: Describe what the image actually shows, not just generic labels like "image" or "photo"
• Keep it concise: Aim for 125 characters or less whilst remaining clear and meaningful
• Include relevant keywords: Naturally work in keywords when they accurately describe the image
• Avoid keyword stuffing: Never overload descriptions with keywords—they must sound natural
• Skip redundant phrases: Don't start with "image of" since screen readers already announce images
• Be specific: Use precise descriptions like "red sports car" rather than just "car"
• Handle decorative images properly: For purely decorative images, use empty alt attributes

Key Takeaway

Alt text serves two equally important purposes: improving web accessibility and helping search engines understand your images. Well-written descriptions that naturally incorporate relevant keywords enhance both user experience and SEO performance. Focus on clarity and accuracy when describing what each image shows. Every important image on your website should have a meaningful, descriptive alternative text attribute that serves both human visitors and search engine crawlers effectively.

Alt Text Examples

Here are examples comparing poor and effective image descriptions:

• Poor: "image," "photo," "picture," "graphic," "img_4729"
• Good: "Blue running trainers on wooden floor," "Professional headshot of smiling woman in grey suit," "Graph showing 40% increase in website traffic"
• With keywords: "Affordable blue running trainers for marathon training," "SEO consultant reviewing Google Analytics dashboard"

Alt Text and Web Accessibility

Beyond SEO benefits, alternative text is essential for web accessibility. Screen readers used by blind and visually impaired individuals read descriptions aloud. Without proper descriptions, users relying on assistive technology cannot understand what your images convey.

Writing effective descriptions creates an inclusive web experience where all users can access your content. This commitment to accessibility improves engagement metrics and can indirectly benefit your SEO through better user experience signals.

Alt Text vs Image File Names

Whilst both file names and alternative text contribute to image SEO, they serve different purposes. File names help search engines locate and categorise images in their systems. Alternative text provides detailed context about image content for both search engines and users.

Best practice is optimising both elements: use descriptive file names like "blue-running-trainers.jpg" and write meaningful descriptions. Together, these elements help search engines fully understand your images and improve your overall search visibility.

Alt Text for Different Image Types

Different image types require tailored approaches when writing descriptions:

• Product images: Include product name, key features, and colour in descriptions
• Infographics: Summarise main data points and the infographic's purpose
• Screenshots: Describe what's shown and its relevance to your content
• Charts and graphs: Summarise the data and trends displayed
• Logos: Simply identify the brand name
• Decorative images: Use empty alt attributes (alt="") for purely decorative elements

Related SEO Terms

• Image SEO — Optimising images for search engines including alt text
• On-Page SEO — Page-level optimisation including image elements
• Web Accessibility — Making websites usable for people with disabilities
• HTML — Markup language where alt attributes are defined
• Screen Reader — Assistive technology that reads alt text aloud

Need Help Optimising Your Images?

Our SEO experts can help you optimise all elements of your website, including image descriptions, to improve rankings and accessibility.