This validator checks if inputed address is an ERC-721 smart contract and if so checks if its safeTransferFrom function is correctly implemented.
We assume that you have Metamask installed and you are on mainnet. It will not cost you any gas to validate any smart contrac, even though these transactions are run using the network.
For your convenience here are some smart contract that you can just copy-paste to test:
||CryptoKitties smart contract. It is pre ERC-721 standard.
||Su Squares smart contract. It is ERC-721 and implements enumerable extensions so all test will start automatically.
||Decentraland smart contract. It is ERC-721 but does not implement enumerable so you will get a prompt to input a valid token id.