Write alt text to explain what an image contributes in its specific page context—not simply to list what appears in it. Informative images need a concise description of their meaning; decorative images need an empty alt value; image-only controls need wording for their action or destination; and complex visuals need a short label plus an accessible text equivalent for the details.
Start by identifying the image’s purpose
The same image can need different alt text—or none—depending on why it appears on the page. Ask what a reader would miss if the image were unavailable, and whether nearby text already supplies that information. W3C’s Web Accessibility Initiative (WAI) explains that images need text alternatives describing the information or function they represent in its Images Tutorial.
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- Informative: conveys meaning or information that matters to the page.
- Decorative or redundant: adds no information, or repeats information already given nearby.
- Functional: acts as a link or control.
- Complex: presents substantial data or relationships, as in a chart or diagram.
These are purpose-based treatments, not labels to include in the alt text itself.
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Describe the essential meaning the image contributes to this page. A literal inventory can be less useful than identifying the relevant action, subject, or information. WAI’s guidance on informative images says the alternative should convey the displayed meaning or content, which typically is not a literal description.
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For example, if an article uses a photograph to illustrate a specific action it explains, name that action or relevant detail rather than writing only “photo of people.” The surrounding text determines what matters; there is no universal caption that works in every context.
When to use empty alt text
For a purely decorative image, or one whose information is already conveyed in nearby text, set an empty alternative: alt="". This lets assistive technology skip the image rather than announce content that does not help the reader. For example:
<img src="topinfo_bg.png" alt="">Do not omit the alt attribute. WAI notes in its decorative images guidance that some screen readers may announce the image’s filename when no alternative is provided. Nor should you write “decorative image”: the empty value is the signal to skip it.
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Alt text for linked images and controls
When an image is the only content of a link or control, describe what activating it does or where it leads—not just what it looks like. WAI’s functional images guidance gives examples such as “Print this page” instead of “printer,” “Search” instead of “magnifying lens,” and “Example.com homepage” instead of “Example.com logo.”
Apply the same principle to a logo that links to a home page: its alternative should communicate the destination. If adjacent link text already identifies that destination and the image adds no new information, consider whether the image is redundant in that context.
How to handle charts, diagrams, and other complex images
Keep the alt text concise: identify the kind of graphic and its subject. Make the detailed information available separately in an accessible text equivalent, such as nearby prose, a data table, or another appropriate description. WAI’s complex images guidance gives this chart description as an example: “Bar chart showing monthly and total visitors for the first quarter 2025 for sites 1 to 3.” The chart’s data and relationships need a fuller equivalent than that short label.
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Do not squeeze every value or a long explanation into the alt attribute. Explain the main takeaway in the surrounding article when that is what readers need, and make the underlying details available as text. Section508.gov also advises against repeating chart trends in alt text when a paragraph below already describes them in its guidance on authoring meaningful alternative text.
Keep alt text concise and avoid repetition
Use the shortest wording that conveys the image’s purpose. WAI’s tips and tricks guidance recommends the most concise description possible; if the needed explanation is longer than a short phrase or sentence, provide a long description instead. Use nearby text to avoid repeating information, but do not leave out meaning a reader needs from the image.
Quick Recap
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| Image role | What the alternative should do | Typical treatment |
|---|---|---|
| Informative | Convey the essential information or meaning | Short, context-specific description |
| Decorative or redundant | Avoid adding noise | Empty value: alt="" |
| Functional | Communicate action or destination | For example, “Search,” “Print this page,” or destination wording |
| Complex | Identify the graphic and provide access to its details | Short alt text plus a longer text equivalent |
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