wanghaisheng Alt Text Design
Write alt text that conveys the same information and purpose as the visual content — not just what the image looks like, but what it communicates.
Core Principle
Alt text answers the question: if this image disappeared, what information would be lost? That's what needs to be in the alt text.
Decision Tree
1. Is the image purely decorative?
- Background textures, dividers, visual flourishes
- Images that repeat information already in adjacent text
- Action: use empty alt (alt="") so screen readers skip it
2. Is the image functional?
- A linked logo, an icon button, an image link
- Action: alt text describes the function, not the image
- Logo linking to homepage: alt="Company name — home"
- Search icon button: alt="Search"
- NOT alt="magnifying glass icon"
3. Is the image informative?
- Photos, illustrations, screenshots that add information
- Action: describe the information the image conveys
- Photo of a damaged product: alt="Crack running along the bottom edge of the screen"
- NOT alt="Photo of a phone" or alt="product-image-032.jpg"
4. Is the image complex?
- Charts, graphs, diagrams, infographics, maps
- Action: short alt text summarising the key message PLUS a longer description nearby (in the page text or a linked detail)
- Bar chart: alt="Bar chart showing sales growth — details below" followed by a text summary of the data
- NOT alt="bar chart" and not the entire data set in the alt attribute
Writing Good Alt Text
Be Specific
- Bad: "A group of people"
- Good: "Three team members reviewing a prototype on a whiteboard"
Convey Purpose, Not Just Appearance
- Bad: "Red circle with a number"
- Good: "3 unread notifications"
Match the Context
The same image needs different alt text in different contexts:
- On a recipe page: "Finished risotto in a white bowl, garnished with parmesan and basil"
- On a kitchenware product page: "Round white ceramic serving bowl, 22cm diameter"
Keep It Concise
- Aim for one sentence, two at most
- Don't start with "Image of..." or "Picture of..." — screen readers already announce it as an image
- For complex images: keep alt text short and provide detail elsewhere
Specific Content Types
Charts and Graphs
- Alt text: state the type and the key takeaway
- Provide a text summary or data table nearby
- "Line chart showing website traffic doubling between January and June 2026. Full data in the table below."
Screenshots
- Describe what the screenshot shows that matters to the reader
- "Settings panel with the notifications toggle switched off"
- NOT "Screenshot of the settings page"
Icons with Labels
- If the icon has a visible text label, the icon is decorative (alt="")
- If the icon is the only indicator, the alt text must convey the meaning
Images of Text
- Avoid images of text wherever possible — use real text
- If unavoidable: the alt text must contain the full text in the image
Assessment Questions
- Does every non-decorative image have meaningful alt text?
- Does the alt text convey purpose, not just appearance?
- Are decorative images marked with empty alt?
- Do complex images have both short alt text and a longer description?
- Would someone using a screen reader get the same information as someone seeing the image?