It’s important because it helps people who can’t see them understand what the visuals are showing or adding to the content. Alt text is usually read by screen readers, not by sighted readers.
Here’s why it matters:
- For people using screen readers: Screen readers don’t describe images – they read out the alt text. The alt text gives it the words to say about what the image shows.
- It explains visually presented information: If an image helps explain something, like a chart with data or a process diagram, the alt text should describe it. This way, people who can’t see the image still understand what it’s showing.
Imagine you’re reading instructions to build something, and it says, “Refer to the diagram below,” but you can’t see the diagram. Without a description, it’s like trying to follow directions in the dark. Alt text shines a light on what’s missing, making sure no one gets left behind. That’s why it’s a crucial part of accessibility in documents.
Tips for writing alt text
- Don’t use it on images that don’t convey any information or are visual padding, you can mark them as decorative.
- When possible, put the information in the written content as a description. Use tables for data shown in charts. The image then becomes decorative.
- Focus on the important details: Start with the most important information first.
- Be specific and concise: Describe the content and purpose of the image (e.g., “A bar chart showing revenue growth from 2020 to 2023 from fifteen million dollars to eighteen point five million dollars”)
- Don’t use phrases like “Image of” or “Picture of”—Word already identifies it as an image.