Basically, similar principles apply to long descriptions in the Play Store and the App Store: The description can help convince potential users to download an app by explaining in more detail what the app is about, what functionalities it contains, and what added value it brings. It is important that the description is easy to read: line breaks, short paragraphs or bullet points can help. It should also be communicated in the tone of voice of the brand.
Since a large part of the description is hidden for the time being, the first 250 or so characters in particular should get to the point and grab the reader*s attention. We recommend that at least 1000 of the available 3000 characters are utilized.
Keyword Density in the Play Store
The Play Store description is taken into account by the store algorithm for ranking and contributes significantly to the discoverability of an app in the Play Store. Therefore, relevant keywords should appear around 3-5 times in the description so that they are classified as relevant by the algorithm (keyword density). Keyword stuffing - mentioning the same word too often - should be avoided, however.
Relevance for iTunes Page in the Apple App Store
In the Apple App Store, the long description is not indexed. However, this does not mean that it should be neglected - it is used for ranking the iTunes App Page, for which "regular" SEO principles apply. Therefore, we recommend to use at least 1000 of the 3000 available characters for the long description in the Apple App Store as well and to integrate the most important keywords.
Apart from that, the long description naturally helps to arouse the interest of potential users, to explain the most important information about the app and thus to persuade them to download it.