The Key Tool is a transparent & secret key derivation tool based on BIP32/39/44 and ZIP32.
It is similar to the Mnemonic Code Converter but built specifically for Zcash and Ycash.
With the Key Tool, you can extract the private keys of most (all?) wallets, as long as they use a seed phrase.
However, the derivation path they use varies from wallet to wallet.
Transparent Wallets follow BIP32/44 and derive the secret key at
m/44'/133'/account'/external/address (133 is for Zcash)
For example, the external address #2 of account #5
The change address is at
Usually, they increase the address index automatically to avoid reusing the same address. The account index is incremented when the user creates a new account for the same currency.
Shielded Wallets follow ZIP32 and derive the secret key at
If you leave the address field empty, the Key Tool will generate the first type of path.
Zcashd has support for ZIP316 (Unified Addresses) and generates its legacy sapling addresses backward from the end to avoid clashing with UA.
Therefore the first sapling address in Zcashd 5.0.0 is at index 2,147,483,647 and then will go down.
Pre-5.0.0 addresses are not supported.
Once you have the secret keys you can import them into YWallet as regular accounts.
Using the Key Tool requires fingerprint/pin authentication.