IP Finder displays the addressing information for an Android device, showing the local address assigned on the current network alongside the public address that remote services observe, together with the connection type and provider.
Presenting both together is the reason to use it, because the difference between them is the thing that actually matters when something is unreachable. The local address is what other devices on the same network use to reach the phone, and it comes from the local router, while the public address is what a remote server sees, and on almost every network it belongs to the router rather than to the device. Understanding that a phone on mobile data frequently sits behind provider level address translation, so its public address is shared with many other subscribers, explains why inbound connections are impossible on such a connection regardless of any configuration. The provider and connection type shown alongside answers the related question of which path traffic is taking, which is useful when a device has both a wireless and a mobile connection available and it is not obvious which one is in use.
The scope is deliberately small and it does not attempt diagnosis, so anything beyond reading current state needs a different tool. For confirming what the device thinks its addressing is, it does the job in one screen.
Link: IP Finder on Google Play