Free Tool

Alt Text Checker

Q: What is the difference between missing alt and empty alt?

Missing alt means the img tag has no alt attribute at all. Screen readers may read the filename or URL, confusing users. Empty alt (alt="") explicitly tells screen readers to skip the image. Use empty alt only for decorative images that add no information.

Q: How long should alt text be?

Keep alt text under 125 characters. Screen readers may truncate or split longer text. If an image needs a detailed description, use a short alt attribute and provide the full description in surrounding text or a longdesc link.

Q: Does alt text affect SEO?

Yes. Google uses alt text to understand image content for Google Images ranking and as a contextual signal for the surrounding page content. Well-written alt text that naturally describes the image can improve visibility in image search results.

Q: Can I test localhost or staging URLs?

Staging URLs work if they are publicly accessible. Localhost URLs will not work because the server-side fetch cannot reach your local machine. For local testing, use your browser's developer tools to inspect image alt attributes.

An alt text checker scans any URL for missing image alt text and flags accessibility gaps that screen readers cannot describe and search engines cannot index. OverlayQA's free alt text checker extracts all images, shows which have alt text and which are missing it, detects filenames used as alt text, and flags redundant phrases. No account required.

What Is Alt Text?

Alt text (alternative text) is the alt attribute on an HTML img tag. It describes the image content in plain text so screen readers can convey the information to users who cannot see the image. When an image fails to load, the browser displays the alt text as a fallback. Search engines also use alt text to understand image content for ranking. WCAG Success Criterion 1.1.1 (Non-text Content) requires text alternatives for all non-decorative images.

How to Check Image Alt Text

Enter your URL. Paste any publicly accessible URL into the input field.
Click Check Alt Text. The tool fetches the page's HTML and extracts all image tags.
Review the image list. See every image with its alt text status: present, empty, missing, or decorative.
Fix reported issues. Add descriptive alt text to images missing it. Mark decorative images with alt="". Re-check to verify.

How to Write Good Alt Text

Be specific and concise. Describe what the image shows in one or two sentences. Aim for under 125 characters.
Skip "image of" or "photo of". Screen readers already announce "image" before reading the alt text.
Describe function, not appearance. For a button icon, describe what it does, not what it looks like.
Use empty alt for decorative images. Purely decorative images should use alt="" to tell screen readers to skip them.
Don't stuff keywords. Alt text is for users, not SEO manipulation. Write natural descriptions.
Include text in images. If the image contains text, include that text in the alt attribute.

Alt Text Decision Guide

Image type	Alt text	Example
Informative image	Describe the content	alt="Bar chart showing 40% increase in Q3 revenue"
Functional image	Describe the action	alt="Download PDF report"
Decorative image	Empty alt	alt=""
Image of text	Include the text	alt="Sale: 50% off all items through Friday"
Complex image	Short alt + long description	alt="Q3 results" with detailed caption below
Logo	Company or brand name	alt="OverlayQA"

Frequently Asked Questions

Is this alt text checker free? Yes. Paste any URL and check as many pages as you need. No account, no login, no usage limits.

Why is alt text important for accessibility? Screen readers read alt text aloud to describe images to users who cannot see them. Without alt text, screen readers either skip the image or read the filename. WCAG 1.1.1 requires text alternatives for all non-decorative images.

What is the difference between missing alt and empty alt? Missing alt means no alt attribute at all. Empty alt (alt="") tells screen readers to skip the image. Use empty alt only for decorative images.

How long should alt text be? Under 125 characters. Use surrounding text or longdesc for detailed descriptions.

Does alt text affect SEO? Yes. Google uses alt text for image search ranking and page context signals.

Can I test localhost or staging URLs? Staging URLs work if publicly accessible. Localhost URLs will not work. Use browser developer tools for local testing.

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Last updated June 2026