An alt tag, also known as alternative text or an alt attribute, is a short description added to an image in HTML. It plays a key role in web accessibility by helping screen readers describe images to visually impaired users. Alt tags also provide SEO benefits, helping search engines understand image content and improving a website’s ranking. Additionally, they serve as fallback text when images fail to load, ensuring users still receive important context.

Definition of an alt tag

An alt tag is a piece of HTML code used to describe an image. It serves three primary purposes:

• Accessibility – Screen readers rely on alt text to convey image content to visually impaired users.
• SEO enhancement – Search engines use alt text to index images, which can improve rankings and visibility in image searches.
• Fallback content – If an image fails to load, the alt tag ensures users still understand what should be displayed.

For example, in HTML, an image with an alt tag might look like this :

<img src="mountain.jpg" alt="Snow-covered mountain under a clear blue sky">

Why alt tags are important

Web accessibility

Web Content Accessibility Guidelines (WCAG) emphasize the need for alt tags to help visually impaired users understand images through screen readers. Without alt text, these users miss out on important visual details.

Search engine optimization (SEO)

Search engines like Google use alt tags to understand an image’s content, making it easier for images to appear in search results. Including relevant keywords in a natural way can boost SEO without keyword stuffing.

Better user experience

Alt text provides context when images don’t load due to slow connections or technical errors. This ensures users still get the information they need.

How to write effective alt tags

Well-written alt text is clear, concise, and descriptive. Follow these best practices to maximize its effectiveness:

Be descriptive yet concise

Describe what’s in the image without unnecessary detail. Instead of "dog," a better alt tag would be "Golden retriever running on the beach."

Use keywords naturally

If relevant, include keywords that align with your page’s content. However, avoid keyword stuffing, which can harm readability and SEO.

Keep it under 125 characters

Most screen readers cut off alt text after 125 characters. Stick to the essential details.

Use alt tags for informational images only

Decorative images (like background patterns) don’t need alt text. Instead, use an empty alt attribute:

<img src="background.png" alt="">

This tells screen readers to ignore the image.

Include context when necessary

If an image is part of a link, the alt text should describe what the user will find after clicking. For example:

<a href="recipes.html"><img src="pancakes.jpg" alt="Homemade pancake recipe"></a>

How to check if your images have alt tags

To verify whether your website’s images have alt text:

• Inspect the HTML – Right-click on an image, select "Inspect," and check for an alt attribute in the tag.
• Use browser extensions – Tools like WAVE or Siteimprove can scan for missing or ineffective alt text.
• Check with Google Lighthouse – This tool provides SEO and accessibility insights, highlighting any missing alt tags.

What happens when alt tags are missing

If an image lacks alt text, several issues can arise:

• Accessibility barrier – Visually impaired users won’t receive any description of the image.
• SEO impact – Search engines won’t be able to properly index and rank the image.
• User experience issues – When an image doesn’t load, users won’t know what was supposed to be there.

FAQs about alt tags

What’s the difference between alt tags and title tags?

Alt tags describe images for screen readers and SEO, while title tags appear as tooltips when users hover over an image.

Do all images need alt text?

No. Essential images (like product photos or infographics) require alt text, but decorative images can use an empty alt attribute (alt="").

Can alt tags improve my website’s SEO?

Yes! Proper alt text helps search engines understand images, boosting your chances of appearing in Google Image search results.

How can I test my site for missing alt tags?

You can manually inspect your HTML, use accessibility tools like WAVE, or run an SEO audit with Google Lighthouse.

How often should I update alt tags?

Review them periodically, especially when updating images, optimizing for SEO, or improving accessibility.

Make your website more accessible and SEO-friendly

Adding effective alt text to your images is a small step that makes a big difference. Whether you're optimizing for accessibility or improving SEO, well-crafted alt tags help both users and search engines understand your content. Ready to optimize your site? Get started today!