What is Alt Text?
Alt Text is a written description added to an image’s HTML or content management system so screen readers and search engines can understand the image’s purpose. Alt Text appears when an image can't load and should convey essential meaning, function, or information without describing decorative details that add no value.
Quick Facts About Alt Text
Category
Web accessibility and on-page content
Used for
Describing image purpose and meaning
Relevant standard
WCAG 2.2 Success Criterion 1.1.1
Common confusion
Alt Text is not the same as an image caption
Also called
Alternative text, Image alt text
Often discussed with
On-Page SEO, Technical SEO
Key Takeaways About Alt Text
- Describe the image’s purpose and essential meaning, not every visible detail.
- Screen readers usually read Alt Text aloud when users encounter an image.
- Decorative images generally need empty Alt Text rather than invented descriptions.
- Alt Text can support image understanding. But it is not a keyword field.
- Product, instructional, and functional images require especially precise descriptions.
Understanding Alt Text
Alt Text is alternative text. It communicates an image’s meaning when unseen. It's commonly stored in an HTML image element’s alt attribute. Content management systems often provide a dedicated field. A screen reader may read the text aloud. A browser may display it when an image fails to load.
Related glossary terms: Structured Data.
Effective Alt Text describes an image’s purpose within its content. A photograph supporting a news story may need a short event description. A product image may need the product name and key feature. The correct wording depends on context. The same image may need different descriptions on different pages.
How Alt Text Works, Is Measured, or Is Used?
Assistive technology can use Alt Text as the main text alternative. Authors should write a brief, specific description. It should provide information a sighted reader needs to understand the page. The description shouldn't begin with “image of” unless useful context requires it.
Alt Text has no universal character-count formula or single scoring metric. Reviewers check whether the text serves the image’s function. They also check the relevant Web Content Accessibility Guidelines. This includes WCAG Success Criterion 1.1.1. A practical review asks three questions.
- What information does the image communicate.
- Why is the image present on this page.
- What would be lost if the image were unavailable.
Informative images need meaningful descriptions. Functional images need text that identifies their action. For example, a search button may use “Search” as Alt Text. It doesn't need a description of the magnifying-glass shape. Decorative images should normally use an empty Alt Text value. Write it as alt="". Assistive technology can then skip them without unnecessary content.
Why Alt Text Matters?
Alt Text improves access for people who are blind or have low vision. This matters when images contain essential information. It also provides a useful fallback when files fail to load. Files may fail because of a weak connection, incorrect path, or technical error. Clear descriptions can help search systems interpret image content. Alt Text alone doesn't determine image rankings.
Good Alt Text also improves content quality. It requires a clear decision about an image’s role. It can show whether an image is genuinely useful. It can also reveal repeated, irrelevant, or poorly labelled visuals. Over-optimised descriptions may reduce accessibility. They may add keywords that don't match the image or its content.
When Alt Text Matters Most?
Alt Text deserves special attention on ecommerce product pages, service pages, forms, charts, maps, and instructional content. A product image may communicate colour or design. A chart may need a nearby text summary of its main conclusion. Images acting as links or controls need descriptions. These descriptions should explain their destination or action.
Alt Text is also important during accessibility reviews, website migrations, and content audits. Teams should check new images and older templates. Repeated omissions often arise from reusable components. A professional review should consider context, keyboard access, captions, surrounding text, and image quality. It shouldn't treat Alt Text as an isolated field.
How to Evaluate Alt Text?
- Check whether every informative image has a useful text alternative.
- Confirm that functional images describe the action or destination rather than their visual shape.
- Review whether decorative images use empty Alt Text and are skipped by screen readers.
- Remove keyword stuffing, repeated captions, and descriptions unrelated to the page context.
- Test representative pages with a screen reader or an accessibility auditing tool.
Related Concepts Compared
Alt Text vs. Image Caption
A caption is visible to most visitors and adds context below or beside an image. Alt Text is primarily an alternative for people who cannot access the image itself.
Alt Text vs. Image Title Attribute
A title attribute may provide a browser tooltip, but it is not a dependable substitute for Alt Text. Accessibility guidance places the essential text alternative in the image’s alt attribute.
Alt Text vs. Long Description
A long description provides detailed information for complex images such as charts or diagrams. Alt Text should remain concise and can point to, or work alongside, a fuller explanation in nearby content.
Alt Text vs. Image File Name
A file name helps organise and identify an uploaded asset, but it is not normally the text alternative read by assistive technology. The Alt Text must communicate the image’s purpose directly.
Expert Note
Alt Text should be written after considering the image and its surrounding copy together. A technically accurate description can still be unhelpful if it repeats a nearby caption, omits an important action, or describes details that do not support the page’s purpose.
Common Mistakes or Myths About Alt Text
- Stuffing keywords into descriptions that do not accurately match the image.
- Writing “image of” for every image without explaining its useful purpose.
- Leaving informative images without Alt Text.
- Using a visible caption as though it automatically replaces an image’s text alternative.
- Adding detailed descriptions to purely decorative images that should be skipped.
Alt Text in Practice: A Real-World Example
A South Brisbane restaurant publishes a photograph of its accessible entrance on a location page. Useful Alt Text could be “Ramp entrance beside the main doorway at the South Brisbane restaurant.” The wording identifies the feature that matters instead of listing every visible object.
Sources & Further Reading on Alt Text
- Alternative Text, MDN Web Docs
- Image SEO Best Practices, Google Search Central
Related Services
Related Terms
Structured Data
Structured Data is a standardised format that labels information on a web page so search engines…
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