Images make websites engaging, but search engines and assistive technologies cannot see them the way people do. They rely on text to understand what an image shows. The alt attribute, often called an alt tag or alt text, provides that description. Well-written alt text helps visually impaired users understand your content, improves your chances of ranking in image search, and adds relevant context to your pages. Poorly written or missing alt text, on the other hand, is a missed opportunity and an accessibility barrier. This guide explains how to write alt tags that serve both people and search engines.
How AAMAX.CO Optimises Images for Accessibility and SEO
AAMAX.CO is a full-service digital marketing company offering web development, digital marketing, and SEO services worldwide. Their team treats image optimisation as an essential part of on-page SEO and accessibility. Through their search engine optimization services, they audit websites for missing and low-quality alt text, write descriptive alt attributes aligned with page topics, compress and properly size images, and implement modern formats for faster loading. Their developers can also build content workflows that make it easy for clients to add accurate alt text whenever new images are uploaded.
What Is an Alt Tag?
Technically, alt is an attribute of the HTML image element rather than a separate tag, but the terms alt tag, alt attribute, and alt text are used interchangeably. The alt attribute contains a short text description of the image. Screen readers read this text aloud to users who cannot see the image. If an image fails to load, browsers display the alt text in its place. Search engines use it, along with surrounding content and file names, to understand what the image depicts.
Why Alt Text Matters for SEO
Google has confirmed that alt text is one of the most important signals it uses to understand images. Descriptive alt text improves your chances of appearing in Google Images and other visual search features, which can drive meaningful traffic for ecommerce, recipes, travel, design, and many other niches. Alt text also contributes contextual relevance to the page as a whole, reinforcing the topic you are targeting. When an image is used as a link, its alt text functions like anchor text, helping search engines understand the linked page.
Why Alt Text Matters for Accessibility
Beyond SEO, alt text is a core accessibility requirement under the Web Content Accessibility Guidelines. Millions of people use screen readers to browse the web. Without alt text, they may hear only a file name or nothing at all, missing information that sighted users take for granted. Accessible websites reach wider audiences, reduce legal risk, and demonstrate care for all users. Importantly, writing for accessibility first usually produces the best SEO results as well.
How to Write Effective Alt Text
Start by describing what the image shows as clearly and specifically as possible. Imagine explaining the image to someone over the phone. Instead of writing dog, write golden retriever puppy playing with a red ball on grass. Specific descriptions provide more useful information to users and more context to search engines.
Keep it concise. Most screen readers handle long text, but a practical guideline is around 125 characters or fewer. Focus on the most important details rather than describing every element.
Consider the context of the page. The same image might need different alt text depending on why it is used. A photo of a person in a running shoe might be described as woman jogging along a coastal path on a fitness blog, but as lightweight blue trail running shoe on a runner's foot on a product page.
Include Keywords Naturally
If a relevant keyword genuinely describes the image, include it naturally. For example, on a page about handmade ceramic mugs, an alt text of handmade ceramic mug with speckled glaze is both accurate and keyword-relevant. Do not force keywords into images where they do not fit, and never stuff multiple keywords into a single alt attribute. Keyword stuffing creates a poor experience for screen reader users and can be viewed as spam by search engines.
Avoid Redundant Phrases
There is no need to start alt text with phrases such as image of or picture of. Screen readers already announce that the element is an image. Get straight to the description. The exception is when the medium matters, such as a painting, illustration, screenshot, or diagram, in which case naming it adds useful context.
Handling Different Types of Images
Informative images that convey content should have descriptive alt text. Functional images, such as icons used as buttons or links, should describe the action rather than the appearance, for example search or download brochure. Images containing text, such as infographics or banners, should include the essential text in the alt attribute or be accompanied by an on-page text equivalent. Complex images such as charts and graphs should have a brief alt description plus a longer explanation nearby on the page.
When to Use Empty Alt Text
Purely decorative images, such as background patterns, spacers, or visual flourishes that add no information, should use an empty alt attribute, written as alt with empty quotes. This tells screen readers to skip the image, reducing noise for users. Do not omit the alt attribute entirely, because some screen readers will then read the file name instead.
Supporting Alt Text With Other Image SEO Practices
Alt text works best alongside other image optimisations. Use descriptive file names such as ceramic-mug-speckled-glaze.jpg rather than generic camera names. Place images near relevant text and add captions where helpful, since captions are widely read. Compress images and serve modern formats such as WebP or AVIF to improve page speed. Specify width and height to prevent layout shifts, and use lazy loading for images below the fold.
Auditing Your Existing Alt Text
Crawling tools and accessibility checkers can identify images missing alt attributes across your site. Prioritise important pages such as product listings, service pages, and high-traffic blog posts. Update vague or keyword-stuffed alt text with clear, accurate descriptions. Build alt text into your publishing checklist so every new image is handled correctly.
Conclusion
Writing an alt tag for SEO is ultimately about describing images accurately, concisely, and in context. When you prioritise the needs of users who rely on screen readers, you also give search engines the information they need to rank your images and understand your pages. Combined with good file names, compression, and placement, strong alt text becomes a small but powerful part of your SEO. For a complete image and on-page optimisation strategy, AAMAX.CO can help ensure every visual on your website works harder for visibility and accessibility.
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