UDP Sender / Receiver is a free utility app available on Android 9.0 and developed by JC Accounting Innovative Technologies Inc. This app allows you to send UDP datagrams to another client or listen for UDP packets. You can send messages as either ASCII or HEX.

The app has two modes: Send/Receive and Receive Only. The former allows you to send UDP datagrams and listen for a response based on the timeout you set, while the latter listens indefinitely for UDP packets and outputs the result in the response section. One of the significant advantages of this app is that it allows you to specify the local port to bind to, which is useful for diagnosing NAT problems (Full Cone Nat, Port Restricted NAT, or Symmetric NAT). Additionally, the app outputs the sender (destination) IP and port of the datagram received, which is useful for diagnosing NAT problems. The app also gets and displays your local IP by clicking the overflow action item and selecting "My IP Address."

Lastly, the app saves the local port, remote IP, and remote port to the application's preferences. If you find the app useful, please like or comment.