The "Alt text" (i.e., alternative text) field on images and icons adds a machine-readable description that is not otherwise visible on the page.
There are two key reasons to add these descriptions to images:
- It improves accessibility for the vision-impaired by allowing a voice-over description of images.
- It improves SEO by giving Google more information to understand your app, and it will help your app rank higher in image searches.
Adding alt text is straightforward. There is a new (optional) "alt text" field under most platform images and icons.
Best practices for adding alt text:
- Be succinct. Many screen readers cut off after 125 characters, and a few words are often enough.
- Do not begin with "Image of…" because the screen reader will add this information. If it's a photo of a black Nike running shoe, add "black Nike running shoe".
- If there is text in the image that is important to the experience, add it to the alt text.
- Do not add text to decorative images.
- Add keywords that help Google to understand your page but do so in moderation and as a part of an accurate description. The alt text field is not the place to add a list of keywords.
- For captioned images, there is no need to repeat the caption in the alt text. The user, screen reader, and Google can already see this caption. Describe the image as you would to someone not looking at the screen.