Best practices for long alt text and the vision-impaired?

1. How does alt text help visually impaired?
2. What is the preferred length of alt text?

How does alt text help visually impaired?

Alt text allows screen readers to read information about images out loud to users who are blind or and visually impaired. Alternative text is necessary so that people who are blind or visually impaired can still access the information provided by an image and understand the purpose of the image.

What is the preferred length of alt text?

It's advisable to keep alt text at around 125 characters or less. It was previously advised that popular screen readers cut alt text off after around 125 characters.