Alt Text vs. Long Descriptions: What’s the Difference?

Alt text and long descriptions are both used to make images accessible to students who use screen readers, but they serve different purposes. This guide focuses on the differences between alt text and long descriptions, when each is appropriate, and how they work together to support student understanding.

For guidance on how to write effective alt text and long descriptions, see Writing Alt Text and Long Descriptions.

Who Uses Alt Text and Long Descriptions?

Alt text and long descriptions primarily support:

• Students who are blind or have low vision
• Students with cognitive or reading-related disabilities
• Neurodivergent students

They can also benefit any student when images fail to load. Additionally, many students who do not require formal accommodations choose to read alt text and long descriptions or use screen readers as an additional way to review and reinforce their learning.

What Is The Difference?

Alt Text

Alt text is a brief substitute for an image, typically limited to around 120 characters.

• Its goal is to capture the essence of the image in context
• It is read automatically by screen readers
• It is also what appears if an image fails to load

Alt text works best for simple images or for giving a high-level overview when a longer explanation is provided elsewhere.

Long Descriptions

Long descriptions are used when an image contains too much information to reasonably fit into alt text.

• Common in science courses, especially for graphs, charts, diagrams, and experimental figures
• Focus on the information students need in order to interpret, analyze, or answer questions
• Should include relevant detail without drifting into decoration or visual trivia

In practice, alt text and long descriptions often work in tandem: the alt text orients the student, and the long description provides additional depth.

A Helpful Metaphor

Think of the alt text as the description of an item on a menu. It is short, but it contains enough information for you to understand the dish. 

• Example: A fish taco with salsa, crema, and cabbage slaw.

The long description is how you would describe the dish to a friend who has never eaten that item. You would want to provide enough relevant information and answer any questions your friend might have about the dish.

• Example: A fish taco containing a battered and fried piece of cod on top of a corn tortilla. The taco is topped with a shredded cabbage slaw and a salsa roja. The salsa consists of tomatoes, onions, and jalapeños, with crema drizzled on top.

Additional Resources

• TLC Guide: Accessibility: Whose Responsibility Is It?
• TLC Guide: Writing Alt Text and Long Descriptions