ERC-721 NFT with OpenZeppelin

• ERC-20: balances (you have 100 KFT). Fungible — every unit is interchangeable.
• ERC-721: ownership of specific IDs (you own tokens #42 and #137). Non-fungible — each token is unique.

solidity
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract CoolCats is ERC721, Ownable {
    uint256 public nextId;

    constructor() ERC721("CoolCats", "CAT") Ownable(msg.sender) {}

    function mint(address to) public onlyOwner returns (uint256) {
        uint256 id = nextId++;
        _safeMint(to, id);
        return id;
    }
}

• ownerOf(tokenId) — who owns a given token
• balanceOf(address) — how many tokens does an address own
• transferFrom, safeTransferFrom
• approve, setApprovalForAll — delegate transfer rights
• _safeMint — internal helper to mint safely (checks the recipient can accept)

NFTs don't store images on-chain (too expensive). They store a URI pointing to a JSON file:

json
{ "name": "Cat #42", "description": "...", "image": "ipfs://..." }

OZ provides ERC721URIStorage if you want per-token URIs, or override _baseURI() for a common prefix.

Write a MintPass ERC-721 with:

• Name "MintPass", symbol "PASS"
• A public mint() function that lets ANYONE mint themselves one token
• Increments nextId on each mint