Accessible eBooks: How to Write Good Alt Text

Alt text (short for alternative text) is a concise, written description of an image that conveys its purpose or meaning to someone who cannot see it. In ePubs, alt text is primarily used for accessibility — screen readers rely on it to describe images aloud to visually impaired users.

Understanding what alt text shouldn’t be is just as important as knowing how to write it and this page will take you through everything you need to know!

TL;DR – Alt Text

• Alt text = a short, meaningful description of an image for readers who can’t see it.
• Keep it under 140 characters (aim for 125 or fewer for accessibility).
• Only include alt text if the image adds new, necessary information.
• Skip alt text if:
  • The image is decorative
  • The image is explained in nearby text or a caption
• Don’t use alt text for:
  • Captions
  • Full explanations
  • Extra details not visible in the image
• Good alt text = a quick answer to:
  • Who, what, where, when, why, or how — in as few words as possible.

🧠 Think: Why is this image here, and what does the reader need to know about it?

When Is Alt Text Required?

As previously mentioned, alt text is primarily used for accessibility. Visually impaired readers rely on screen readers to describe images aloud.

Do include alt text if:

• The image is central to understanding the content
• It conveys new or essential information that isn’t already stated

Do not include alt text if:

• The image is fully explained in the caption or nearby text
• The image is purely decorative

When Should You Not Use Alt Text?

When writing alt text, most people approach the task with the very best intentions, but if you don’t have personal experience with accessibility needs, it can be very difficult to understand the best way to use it…or not use it.

Alt Text Is Not a Caption

Captions are visible to all readers and may provide context, background, or commentary.

Alt text is hidden and should focus only on what a visually impaired reader needs to understand the image’s purpose.

Not a Full Explanation

Alt text should be short and purposeful. If a detailed explanation is needed, include it in a caption or the surrounding body text.

Not a Place for Hidden Details

Don’t include emotional interpretation, historical background, or off-image commentary unless it’s clearly visible in the image itself.

Alt text is a quick summary that answers:

What would someone need to know about this image to understand the content if they can’t see it?

Imagine someone reading your book with images turned off or using a screen reader. Your goal is to capture the essential point of each image — no more, no less.

What Makes a Strong Alt Text Description?

Good Alt Text Should:

• Convey just enough to explain the image’s function or meaning
• Provide clarity about what’s shown, without interpretation
• Create a seamless experience for screen reader users
• Fit within 140 characters or fewer (Amazon’s max; aim for 125 for best usability)
• Avoid quotation marks, acronyms, and excessive punctuation, which can confuse or disrupt screen readers

Alt text should not attempt to describe every visual detail. Instead, a useful technique is to briefly answer any of the relevant:

Who, What, Where, When, Why, or How — in as few words as possible.

The goal is not completeness, and it’s definitely not to add more detail than the image shows. If there’s something important that cannot be seen in the image but is necessary for understanding, that information belongs in a caption or the main body text, not in the alt attribute.

Remember, screen reader users must listen to alt text before they can move on, so long, overly detailed entries become a barrier rather than a help.

Alt Text Formula

If you’re unsure how to write concise alt text, try this simple formula:

[What the image is] + [Key detail(s) or purpose in context]

Examples:

• “Map of France showing WWII battle sites”
• “Author speaking at 2023 book launch”
• “Map of Arda showing mountains, cities, and rivers”

What to Leave Out

• “Image of…” or “Photo of…” → Screen readers already announce that it’s an image.
• Excess visual details → Don’t describe backgrounds, colors, or styling unless meaningful.
• Interpretation or symbolism → Unless it’s visually clear, leave interpretation to the text.

Atticus is designed to meet accessibility guidelines and, as such, there are certain things you can and should include with any images you import, and other things you cannot and should not do with your alt text. We have a tutorial dedicated to helping you master the alt text in your book’s formatting here: Add Alt Text to Images Using Atticus