Images make websites more engaging, but search engines cannot see images the way humans do. They rely on text signals to understand what an image shows, and the most important of these signals is the alt tag, more accurately called alt text or the alt attribute. Writing good alt text improves accessibility for visually impaired users, helps your images appear in image search, and supports the overall relevance of your pages. In this guide, we explain how to do SEO alt tags properly, with practical examples and best practices.
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What Is an Alt Tag?
The alt attribute is a piece of HTML added to an image element that describes the image's content and function. In code, it looks like an img element with an alt attribute containing a short description. If an image fails to load, the browser displays the alt text instead. Screen readers read the alt text aloud to users who cannot see the image. Search engines use it to understand the image and its relationship to the surrounding content.
Why Alt Tags Matter for SEO
Alt text helps search engines index your images correctly, which can lead to traffic from image search results. It also provides additional context about the page topic, reinforcing relevance for your target keywords. Because search engines prioritize accessible, user-friendly websites, proper alt text contributes to an overall quality experience. For ecommerce sites, optimized product image alt text can drive meaningful traffic from shoppers searching visually.
How to Write Effective Alt Text
Be descriptive and specific. Describe what the image actually shows. Instead of writing dog, write golden retriever puppy playing with a red ball on grass. Specific descriptions help both users and search engines understand the image.
Keep it concise. Aim for roughly 125 characters or fewer. Many screen readers cut off longer text, and concise descriptions are easier to understand.
Include keywords naturally. If it makes sense, include your target keyword, but only when it accurately describes the image. For a page about handmade leather wallets, an image might have alt text like handmade brown leather bifold wallet with stitched edges. Never force keywords where they do not belong.
Consider context. The same image might need different alt text depending on the page. A photo of a chef in a kitchen might be described differently on a restaurant's About page versus a culinary school's course page.
Avoid redundant phrases. Do not start with image of or picture of. Screen readers already announce that the element is an image, so these phrases add unnecessary length.
Examples of Good and Bad Alt Text
For a photo of a modern office workspace, poor alt text would be office or image1. Keyword-stuffed alt text would be office desk office furniture best office desk buy office desk. Good alt text would be minimalist white office desk with laptop and potted plant near a window.
For an infographic, alt text should summarize the main takeaway, and the full information should be included in the surrounding page text so all users can access it.
When to Leave Alt Text Empty
Purely decorative images, such as background patterns, spacers, or design flourishes, do not need descriptive alt text. Use an empty alt attribute so screen readers skip them. This improves the experience for assistive technology users by avoiding unnecessary interruptions. However, never omit the alt attribute entirely, as some screen readers will read the file name instead.
Alt Text for Functional Images
If an image acts as a link or button, the alt text should describe its function rather than its appearance. For example, a magnifying glass icon used as a search button should have alt text like search, and a logo that links to the homepage might use the company name followed by home.
How to Add Alt Text on Common Platforms
In WordPress, select an image in the media library or block editor and fill in the Alternative Text field. In Shopify, open a product image and choose the option to add alt text. Most website builders, including Wix and Squarespace, offer an alt text field in image settings. For custom sites, developers add the alt attribute directly in the HTML or through the content management system.
Combine Alt Text With Other Image Optimizations
Alt text works best alongside other image SEO practices. Use descriptive file names, compress images to reduce load times, use modern formats such as WebP, specify width and height to prevent layout shifts, and place images near relevant text. Adding images to your XML sitemap can also help search engines discover them.
Alt Text in an AI-Driven Search World
AI-powered search systems increasingly analyze images and multimodal content. Clear alt text provides reliable context that helps these systems understand and reference your visuals accurately. This is one reason that GEO services include accessibility and structured descriptions as part of optimizing content for generative search. It also makes your visual assets more reusable across broader digital marketing channels.
Final Thoughts
Learning how to do SEO alt tags is simple but valuable. Write specific, concise descriptions that accurately reflect each image, include keywords only when natural, consider context, leave decorative images empty, and describe the function of linked images. Combined with proper file names, compression, and modern formats, good alt text improves accessibility, supports rankings, and helps your images reach more people through search.
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