TL;DR: A short written description of an image, added via the HTML alt attribute, so screen readers and search engines understand what it shows.
In a nutshell
Alt text serves three jobs: accessibility (screen readers narrate it to blind users), SEO (Google uses it to index images), and fallback (it displays if the image fails to load). Example: instead of “image123”, write “Golden retriever running through grass with tennis ball”. Decorative images get empty alt=””.
Quick answer: Alt text (alternative text) is a brief written description of an image, added via the alt attribute in HTML. It serves three purposes: accessibility (screen readers read it to visually impaired users), SEO (Google uses it to understand image content), and fallback (it displays if the image fails to load). Modern SEO benefits substantially from descriptive alt text on every meaningful image.
What Is Alt Text?
Alt text (short for “alternative text”) is an HTML attribute used to describe the content and function of an image on a web page. Its primary purpose is to make images accessible to users who rely on screen readers, but it also plays a significant role in on-page SEO, particularly for image indexing and semantic relevance. See also the related ALT attribute entry.
Why Is Alt Text Important?
There are two main reasons to use alt text:
- Accessibility: It ensures that users with visual impairments can understand image content using assistive technology like screen readers.
- Search Engine Optimisation: Search engines can’t interpret images visually. Alt text helps them understand what each image represents, supporting broader content relevance and visibility in Google Images.
How Alt Text Supports SEO
Alt text enhances your SEO by improving contextual signals and giving your images a chance to rank in image search results. Well-optimised images can bring in organic traffic, especially in visually driven sectors like ecommerce, design, and food & drink. It also pairs with good image optimisation habits like compression and modern formats.
When alt attributes accurately describe an image, search engines use that data to:
- Contextualise the page’s subject matter
- Match images to relevant keyword searches
- Improve accessibility scoring, which may indirectly influence rankings
For example, in our Shopify SEO projects, alt text is crucial for product photos. It helps Google understand what the product is, improving both product page rankings and image visibility.
Alt Text and Accessibility
Alt text is not just about SEO, it’s about inclusivity. For users who rely on screen readers, alt attributes provide a spoken description of the image. This is vital for websites in regulated sectors (finance, healthcare, public services) or brands that value digital accessibility and compliance with the WCAG guidelines.
Writing Great Alt Text
Here’s what good alt text looks like:
- Descriptive: It should clearly describe the image content
- Concise: Ideally under 125 characters
- Contextual: It should relate to the image’s function on the page
- Keyword-friendly: You can use relevant keywords, but only where natural
Examples:
- Weak: “image123”
- Okay: “Dog in park”
- Strong: “Golden retriever running through grass with tennis ball”
How to Add Alt Text
If you’re hand-coding HTML, you’ll add it like this:
<img src="dog.jpg" alt="Golden retriever running through grass with tennis ball">In WordPress with Bricks Builder, alt text can be added via the media library or in the image block settings. CMS platforms like Shopify, Wix, and Squarespace also include alt text fields in their media managers. For broader guidance, see Google’s SEO Starter Guide.
Alt Text in Practice at BrisTechTonic
We check alt text usage as part of every SEO Audit we run. In fact, we’ve found that even sites with excellent content and fast page speed often neglect image optimisation. By updating or writing proper alt text across key pages, we’ve helped clients improve accessibility scores and generate new traffic from image search.
If you’re building your site in-house or managing multiple team members, we recommend including alt text writing in your content creation process and image guidelines. Our SEO Blueprint course includes checklists and real examples of how to implement this effectively at scale.
Alt Text and Website Migrations
Planning a redesign or move to another CMS? Don’t forget alt text. It’s often lost during a website migration, and restoring it page-by-page can be a nightmare. We’ve created a migration-specific image audit process that’s included in our Website Migration service to preserve alt attributes and improve them where needed.
Common Mistakes to Avoid
- Leaving alt text blank (unless the image is purely decorative)
- Using identical alt text across multiple images
- Keyword stuffing (“best SEO agency Bristol SEO SEO”)
- Describing what the image looks like without explaining its purpose
Optimising at Scale
If you’ve got hundreds (or thousands) of images, manually writing alt text can feel overwhelming. That’s why tools like SEOptimer and Screaming Frog are so useful, they allow you to quickly scan for missing alt attributes and fix them in bulk. For ecommerce clients using WooCommerce or Shopify, we often use export/import spreadsheets to handle alt text updates efficiently.
Helpful Tools
- Rank Math SEO Plugin – WordPress-based alt tag auditing
- Screaming Frog – Full-site SEO crawling, including alt attribute checks
- Google PageSpeed Insights – For checking if images are optimised
BrisTechTonic Services That Support Image SEO
Need help putting this into action? We’ve got you covered:
- Technical SEO – Ensures all your markup, including alt tags, is crawlable and correct
- SEO Audits – Identify missing or poor alt text across your entire site
- Ecommerce SEO – Critical if you rely on product imagery
- SEO Blueprint Course – Learn how to build SEO-friendly content from scratch, including images
Explore Related Glossary Terms
External Resources
- Google’s Image SEO Guidelines
- WebAIM Guide to Writing Alt Text
Frequently Asked Questions
How long should alt text be?
Specific enough to describe the image, short enough to be readable. Typically 5-15 words, up to 125 characters. Don’t pad with keywords; describe what the image actually shows. Decorative images (like background patterns) should have empty alt text (alt=””), not no alt attribute.
Should I include keywords in alt text?
Where genuinely relevant, yes. The alt text for a product image should naturally include the product name. The alt text for a stock photo of a person at a laptop probably shouldn’t force keywords in. Honest description first, keywords second when they fit.
Does alt text affect rankings?
Indirectly. Alt text helps Google understand image content, which contributes to overall page topical relevance and image search rankings. The direct effect on text search rankings is small; the effect on image search rankings can be significant for visual products.
What about decorative images?
Use empty alt text: alt=””. This signals to screen readers that the image is decorative and they should skip it. Don’t omit the alt attribute entirely; an empty alt is different from no alt and gives the right signal to assistive technology.
Take this further
Alt text is accessibility and SEO foundations that compound. We audit alt text systematically because most sites have at least some images missing it.
Ready to apply this to your own site? Book a free discovery call, or explore our SEO strategy service.