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xpepermint Merge pull request #117 from MoMannn/master
Gas cost optimization in calculating index size and in usage of safeMath.
Latest commit 19c71e4 Jun 25, 2018

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ERC-721 Token

This is a complete implementation of the ERC-721 non-fungible token standard for the Ethereum blockchain. This is an open source project build with Truffle framework.

Purpose of this implementation is to provide a good starting point for anyone who wants to use and develop non-fungible tokens on the Ethereum blockchain. Instead of re-implementing the ERC-721 yourself you can use this code which has gone through multiple audits and we hope it will be extensively used by the community in the future.

If you are looking for a more feature-rich and advanced ERC721 implementation, then check out the Xcert repository.


Since this is a Truffle project, you will find all tokens in contracts/tokens/ directory. There are multiple implementations and you can select between:

  • NFToken.sol: This is the base ERC-721 token implementation (with the support for ERC-165).
  • NFTokenEnumerable.sol: This implements optional ERC-721 support for enumeration. It is useful if you want to know the total supply of tokens, to query a token by index, etc.
  • NFTokenMetadata.sol: This implements optional ERC-721 meta-data features for the token contract. It implements a token name, a symbol and a distinct URI pointing to a publicly exposed ERC-721 JSON metadata file.

Other files in the directory starting with ERC*.sol are interfaces and define the respective standards.


  • NodeJS 9.0+ recommended.
  • Windows, Linux or Mac OS X.

Using Remix? This package uses NPM modules which are supported in the Remix Alpha version only. You can also use the npm run flatten command to create a build/bundle.sol file with all package contracts which you can manually copy and then paste into Remix editor.



This is an NPM module for Truffle framework. In order to use it as a dependency in your Javascript project, you must install it through the npm command:

$ npm install @0xcert/ethereum-erc721


Clone the repository and install the required npm dependencies:

$ git clone
$ cd ethereum-erc721
$ npm install

Make sure that everything has been set up correctly:

$ npm run test



To interact with package's contracts within JavaScript code, you simply need to require that package's .json files:

const contract = require("@0xcert/ethereum-erc721/build/contracts/NFTokenEnumerable.json");


Creating smart contract

The easiest way to start is to create a new file under contracts/tokens/ (e.g. MyNFToken.sol):

pragma solidity ^0.4.23;

import "../tokens/NFTokenMetadata.sol";
import "@0xcert/ethereum-utils/contracts/ownership/Ownable.sol";

contract MyNFToken is

    string _name,
    string _symbol
    nftName = _name;
    nftSymbol = _symbol;

  function mint(
    address _owner,
    uint256 _id
    super._mint(_owner, _id);

  function burn(
    address _owner,
    uint256 _tokenId
    super._burn(_owner, _tokenId);


That's it. Let's compile the contract:

$ npm run compile

The easiest way to deploy it locally and start interacting with the contract (minting and transferring tokens) is to deploy it on your personal (local) blockchain using Ganache. Follow the steps in the Truffle documentation which are described here.

Deploying on testnet (Ropsten)

Next step is to deploy the contract on the testnet.


  • geth
  • Wallet with some ether.

Create a new file migrations/2_mytoken_migration.js and put in:

const MyNFTokenContract = artifacts.require('./tokens/MyNFToken.sol');

module.exports = function(deployer) {
  deployer.deploy(MyNFTokenContract, 'MyNFTokenTest', 'MYNFT');

Start geth and sync your client with the testnet (can take a little bit):

$ geth console --testnet --light --rpc --rpcaddr "localhost" --rpcport "8545" --rpccorsdomain "*" --rpcapi="db,eth,net,web3,personal,web3"

Open another terminal and create a new account (your "test" account wallet):

$ geth --testnet account new

NOTE: In this example the wallet address is 0x9062dd79d7e4273889b234f6b0c840ca43280af60x9 (make sure you prepend the returned string with 0x yourself). Your account address will be different! And don't forget the passphrase otherwise you won't be able to unlock your new account. Now, go and send some ether to it (you can get some here.

Open project's truffle.js and add the following:

module.exports = {
  networks: {
    'ropsten': {
      host: 'localhost',
      port: 8545,
      network_id: '3', // Ropsten ID 3
      from: '0x9062dd79d7e4273889b234f6b0c840ca43280af60x9', // account address from which to deploy
      gas: 4000000,

Next, let's unlock your account:

$ npm run console -- --network ropsten
truffle(ropsten)> web3.personal.unlockAccount("0x9062dd79d7e4273889b234f6b0c840ca43280af6", "<PASSWORD>", 1500)

At last, deploy the contract:

$ npm run migrate -- --network ropsten

You can now interact with the contract. First get the address of the deployed contract:

$ npm run networks

You can also check it on Ropsten etherscan. Then in the truffle console (second terminal):

> const { abi } = require('./build/contracts/MyNFToken.json');
> const account0 = '0x9062dd79d7e4273889b234f6b0c840ca43280af60x9'; // your unlocked account
> const account1 = '0x294a4c90900c0dae6ce8e3329a2b219a1f3d8c22'; // another account (you can create it)
> const MyNFTokenContract = web3.eth.contract(abi);
> const MyNFTokenInstance =<MyNFToken ADDRESS>);

> MyNFTokenInstance.symbol();
> MyNFTokenInstance.balanceOf(account0).toString();
'0' <-- we don't have any NFTokens yet

>, '1234', { from: account0 });
>, '5678', { from: account0 });
> MyNFTokenInstance.balanceOf(account0).toString();
'2' <-- Now we have 2!

> MyNFTokenInstance.burn(account0, '5678', { from: account0 });
> '0xb2b4eede6793212ac2d085d0d1121ce78da26513dc8c3503dc4faadc2f771f58'
> MyNFTokenInstance.balanceOf(account0).toString();
> MyNFTokenInstance.safeTransferFrom(account0, account1, '1234', { from: account0 });
> MyNFTokenInstance.balanceOf(account0).toString();
> MyNFTokenInstance.balanceOf(account1).toString();


We already deployed some contracts to Ropsten network. You can play with them RIGHT NOW. No need to install software. In this test version of the contract, anybody can mint or burn tokens, so don't use it for anything important.

Contract Token address Transaction hash
NFToken 0xdf8f576057f2f19f8cae4f7ae155a0ee66c05f24 0x665a0dc54b707e6cf354b2521368452ee11c19939b18d60d1df2649ef2a996be
NFTokenEnumerable 0xde0fb829c3562ec9ec68cb4fed1015ee81b81feb 0xb520fceed5284c8d08611dca3768c69f23e5475d3d6b49cfbaa5105b5eeca54a
NFTokenMetadata 0xa3cdc8acd916d99104ab5428bc26372d0039cc86 0xbe1d72cd7f8e5865b3b6f7f95b72019733d8a2f897ff483b212de0a79f01aa40
NFTokenMetadataEnumerable 0x7cc392789d2c0cc61377a26cf4dd181095b402a5 0xe706840e18c43b32a9f33dead9495e961ad91aaaa0ee4f2aa866726ea33c95ea


See for how to help out.


See LICENSE for details.