How do I detect if the app uses React Native, given APK file?

The accepted solution certainly will get you the right answer, but it will be quite slow. It is what I did originally, and it was not fast enough for my needs since I was running this script across hundreds of APKs. I developed an alternate solution and executed it before the original made it through 5% of the APKs.

The reason I don't like checking for layouts having com_facebook in the name (the other pre-existing solution) is that it is entirely plausible for an app to be using another Facebook SDK that contains a layout file starting with that string. I don't know of any false positives, but it seemed reasonably likely that there would be some.

Instead I check for the presence of libreactnativejni.so which I have to imagine only gets used if React Native is being used. (I originally was looking for libyoga.so, but I had a few false positives, I think because there's a logging library by the same name.)

Specifically, this condition on a Mac in a bash script is what I'm using (I think it's portable, but have not tested):

if [ "$(unzip -l $apkfile | grep libreactnativejni.so | wc -l)" -gt "0" ]
then 
echo "Uses RN"
fi

Not sure if this proven way.

Download the apk from the store to your PC, I used APK Downloader FireFox extension (if you don't have the app apk already).

Open apk with Zip software (I am on Linux so I used Ark). Now you can see parts of the project.

Go to res->layout and search for com_facebook..., In my case it was com_facebook_activity_layout.xml. If you have one layout with com_facebook in it then this apk was created with React.

The most simple solution

Open the APK in Android Studio and check the classes.dex-files(can be more the one file). What you are looking for is:

• React Native - do you find folder com\facebook\react ?
• Flutter - do you find folder io\flutter ?
• Xamarin - do you find folder com\xamarin\ ?

It could look like this in Android Studio