Alt Text Checker

Why Alt Text Matters for Accessibility

Alt text (short for "alternative text") is the text equivalent of an image. It is read aloud by screen readers, displayed when images fail to load, and used by search engines to understand visual content. Under WCAG 2.2 Success Criterion 1.1.1 (Non-text Content), every meaningful image must have a text alternative that conveys the same information as the image.

Missing alt text is the second most common WCAG violation found in automated audits, after low colour contrast. The 2025 WebAIM Million study found that 54.5% of all images tested had detectable alt text issues — including missing attributes, empty alt on informative images, and alt text on decorative images that should be hidden from assistive technology.

WCAG Image Requirements

WCAG categorises images into several types, each with different alt text rules:

Informative Images

Images that convey content — photos, illustrations, diagrams — must have alt text that describes their purpose. The alt text should be concise (typically under 125 characters) and should not begin with "Image of" or "Picture of" since screen readers already announce the element as an image.

Decorative Images

Images that are purely decorative — background patterns, spacer GIFs, ornamental borders — must have an empty alt attribute (alt="") so screen readers skip them entirely. Omitting the alt attribute altogether is different from setting it to empty and is a WCAG failure.

Functional Images (Links & Buttons)

Images inside links or buttons must have alt text that describes the action or destination, not the image itself. For example, a magnifying glass icon inside a search button should have alt="Search", not alt="Magnifying glass icon".

Complex Images (Charts, Infographics)

For images whose content cannot be adequately conveyed in a short alt text — like charts, graphs, or infographics — WCAG requires both a brief alt text and a longer description, either in the surrounding text or via aria-describedby.

Common Alt Text Mistakes

• Missing alt attribute entirely — the most common failure. Screen readers may read the file name (e.g., "DSC_0042.jpg") instead.
• Alt text on decorative images — adding alt text to spacers, dividers, or background images clutters the screen reader experience.
• "Image of…" or "Photo of…" prefixes — redundant, since screen readers already announce "image".
• File names as alt text — CMS platforms sometimes auto-fill alt text with the file name. Always review.
• Identical alt text for different images — each image that conveys different information should have unique alt text.

How to Write Good Alt Text

1. Be specific — "CEO Jane Smith speaking at the 2025 Web Summit" is better than "Person at event".
2. Be concise — aim for under 125 characters. If more context is needed, use surrounding text.
3. Describe the purpose, not just the appearance — if the image is a CTA button, describe the action it performs.
4. Skip "image of" or "graphic of" — this is redundant.
5. Mark decorative images with empty alt — <img src="..." alt="" />.

Beyond Alt Text: Full Accessibility Audit

Alt text is just one of dozens of WCAG requirements. For a complete picture of your website's accessibility, run a free Accesseon scan. It checks alt text, colour contrast, form labels, ARIA attributes, keyboard navigation, and 50+ other WCAG 2.2 success criteria — and tells you exactly how to fix each issue.