How to Write Alt Text: A Practical Guide with Examples
Good alt text conveys the purpose of an image in a sentence or less. The trick is matching the description to the image's role — informative, functional, or decorative — and knowing when to leave alt empty.
Alt text (the alt attribute) is what a screen reader announces in place of an image, what shows when an image fails to load, and a genuine SEO signal. Missing or poor alt text is one of the most common — and most easily detected — accessibility failures, which is exactly why it shows up in so many lawsuits.
The core rule: describe purpose, not pixels
Ask what the image communicates in context. A photo of a product on a product page needs the product's name; the same photo as a decorative background needs nothing. Describe the function or information, not every visual detail.
Informative images
These convey content. Describe the essential information concisely.
- Good: alt="Bar chart showing sales doubling from 2024 to 2026"
- Weak: alt="chart" or alt="image of a chart"
Functional images
These do something — a logo that links home, an icon button. Describe the action or destination, not the graphic.
- Good: alt="Search" on a magnifying-glass button
- Good: alt="Acme home" on a logo that links to the homepage
Decorative images
Spacers, background flourishes, and icons that merely repeat adjacent text add no information. Give them an empty alt (alt="") so screen readers skip them — never omit the attribute entirely, or some readers will announce the file name.
Practical do's and don'ts
- Keep it concise — aim for under ~150 characters; use a caption or nearby text for longer descriptions.
- Don't start with "image of" or "picture of" — the screen reader already says it's an image.
- Don't stuff keywords; write naturally for a human listening.
- For complex images (charts, diagrams), provide a short alt plus a longer description nearby.
- If text is inside the image, include that text in the alt.
A scanner can tell you an image is missing alt text. Only a human can tell you whether the alt text is actually meaningful — so do both.
accessibilitywebsite.com flags every image missing alt text during a scan and helps you generate sensible descriptions, so you can clear this category quickly and review the wording for accuracy.
Frequently asked questions
- How long should alt text be?
- Keep it concise — generally under about 150 characters. If an image needs a longer explanation (like a chart), pair a short alt with a fuller description in nearby text or a caption.
- What alt text should decorative images have?
- Use an empty alt attribute (alt="") so assistive technology skips the image. Omitting the attribute entirely can cause some screen readers to read out the file name.
- Should I start alt text with 'image of'?
- No. Screen readers already announce that the element is an image, so phrases like 'image of' or 'picture of' are redundant. Describe the content or function directly.
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