Google’s John Mueller has stated that app interstitials will be problematic when it comes to mobile-first indexing.
For example, if an app interstitial replaces a website’s homepage, then that’s what Google will index in search results.
Clearly that’s an issue as it’s the homepage that should be indexed.
“On the topic of interstitials … With Mobile-First Indexing, an app-interstitial will be problematic. If it’s robotted, your homepage might be too. If it replaces your homepage, that’s what we index.”
Users want to land on a web page when they click on a search result, especially when they’re on a desktop where an app interstitial would be irrelevant.
Most importantly, from an SEO perspective, if Google recognizes an app interstitial as the homepage then it could significantly impact how it’s ranked in search results.
Alternatives to App Interstitials
Mueller points to a Google Webmaster Central blog article that contains examples of acceptable alternatives to app interstitials.
Specifically, the article provides the following suggestion for an acceptable alternative:
“Banners that use a reasonable amount of screen space and are easily dismissible. For example, the app install banners provided by Safari and Chrome are examples of banners that use a reasonable amount of screen space.”
In order to not cause problems with mobile-first indexing, interstitials should be created in a way that search engines can still see the normal content on the web page.
The interstitial should also not cause the page to change URLs when a user, or search engine crawler, lands on it.