Apple app store listing serves three purposes, each of which are important for App Store Optimization:
Apple reviews each app manually and uses the app description to help them determine if the keywords used in the app name and keywords field are relevant. A theme that appears throughout the entire ASO process is targeting relevant keywords and phrases. If an app is targeting words that don’t appear in the description field, Apple may reject the offending keywords from the app name or keywords field, removing any chance of ranking.
The best way to demonstrate keyword relevance is by reinforcing the strengths of your app. Just like in the app name and keywords fields, use search terms your target audience is using. Talk about your features in the language they are using when searching the app store. For example, if the app store data from Gummicube says the target audience is searching for "photo collages" and not "photo albums", or "share photos" and not "send photos", refer to features in the app the way the audience searches for them.
Apple allocates 4,000 characters (around 600 words) for the app description field. Treat this space as a selling opportunity, explaining in detail the features and benefits of the app with a clear call to action. If a potential user is reading an app description, they have already searched, selected from results, viewed the app's icon and are now researching further if the app is a fit. Marketing and sales copy is encouraged.
Open with 1-3 clear and compelling sentences telling a prospective user what the app does and who it is for. Next, introduce the app's features starting with most important. A feature may have several benefits, and the use of bullets makes the description easy to read and understand. Always format for readability, utilizing spacing and bullets as needed. The app description should reinforce the keywords in the app name and keywords fields, should include compelling copy and be used to convert app store views into users. Learn more about app description best practices for 2020.