How to Write Alt Text That Boosts SEO and Accessibility

Alt text (alternative text) is the descriptive text added to an image's HTML alt attribute. It serves two critical purposes: it helps visually impaired users understand images via screen readers, and it helps search engines interpret image content. Writing good alt text improves both accessibility and SEO, yet many websites get it wrong. Here's how to write alt text that works for everyone.

Why Alt Text Matters

• Accessibility: Screen readers rely on alt text to describe images to users who can't see them. Without it, users miss context or hear the image filename, which is rarely helpful.
• SEO: Search engines use alt text to understand what an image depicts, which helps your images appear in image search results. It also contributes to page relevance signals.
• User Experience: If an image fails to load, the alt text is displayed in its place, providing context.

Alt Text Best Practices

1. Be Descriptive and Specific

Describe what the image shows in a clear, concise way. Focus on the essential details. For example:

• Bad: image123.jpg or photo
• Good: A woman working on a laptop in a modern office with natural light
• Better (if relevant to context): A marketing manager analyzing SEO data on a laptop

2. Keep It Concise

Screen readers typically stop reading alt text after around 125 characters. Aim for a short phrase or sentence—usually 5-15 words. Avoid long-winded descriptions.

3. Include Keywords Naturally

If the image is relevant to your page's topic, include your target keyword naturally, but don't force it. Alt text is primarily for description, not keyword stuffing. For example, if your page is about "organic coffee beans," an image of a coffee farm could have alt text: Organic coffee beans growing on a farm in Colombia.

4. Don't Start with "Image of" or "Picture of"

Screen readers already announce that an image is present. Starting with those words is redundant. Jump straight to the description.

5. Use Proper Punctuation

Write in complete sentences or phrases with periods so screen readers pause appropriately. For example: A red bicycle parked against a brick wall.

6. Context Matters

Consider the image's role on the page. A decorative image (like a background pattern) should have empty alt text (alt="") so screen readers ignore it. An informative image (like a chart) needs a thorough description. A functional image (like a search icon that is a link) should describe the action: Search.

7. Avoid Redundancy

If the image is already described in nearby text, you may use a brief alt text. For example, if a photo of a CEO appears next to their name and title, alt text could be simply Jane Doe, CEO.

Common Alt Text Mistakes

• Missing alt attribute: The most common error. Every image must have an alt attribute, even if empty (for decorative images).
• Keyword stuffing: Writing "buy cheap shoes online" for every shoe image hurts UX and can be seen as spammy.
• Being too vague: "Man" instead of "A man smiling while holding a smartphone"
• Repeating the caption: If there's a caption below the image, alt text should still describe the image, not repeat the caption.

How to Check Your Alt Text

• Use a screen reader (like VoiceOver on Mac or NVDA on Windows) to experience your site as a blind user does.
• Run a free website audit to identify missing or poor alt text. Tools can flag images without alt attributes or with overly long alt text.
• Review your images in Google Search Console's image search report to see if they're indexed properly.

Final Checklist

• [ ] Every image has an alt attribute.
• [ ] Decorative images have alt="".
• [ ] Informative images have descriptive alt text.
• [ ] Functional images (links/buttons) describe the action.
• [ ] Alt text is concise (under 125 characters).
• [ ] Keywords are used naturally when relevant.
• [ ] No redundant phrases like "image of".

Writing good alt text takes a little extra time, but it pays off in better accessibility, improved SEO, and a better experience for all users. Start with your most important pages and work through your site systematically. For a full audit of your site's accessibility and SEO issues, run a free audit today.

For more guides on improving your website, visit our guides library.

More guides · Compare audit tools · Run a free website audit