I checked it for a bit (until part where private key is needed) and it's cool tool. Do you have any plan to support testnet?
This is a good idea. I could add this to my list of future improvements. And testnet transactions would also make people feel safer inputting their private key.
And in general for those who were wondering, I null out the private key value after having it sign the transaction. Again, there might be other security mechanisms that I am unaware of.