here are my NFC security tools this time for your Nokia 6131 NFC. The tool set consists out of: BtNfcAdapter (a simple NDEF reader/writer that is controllable via Bluetooth - basically turns your 6131 NFC into a lightweight tag reader/writer), BtNfcAdapterRaw (Mifare Classic raw reading version of BtNfcAdapter), and MfStt (the Mifare Sector Trailer tool, a very basic tag security checker).
All the tools are for educational purposes only! They are not stable! Especially take care when using the writing features of MfStt).
Feedback is welcome as always. I also accept dumps of cool NFC tags (only including a picture of that very tag).