🤖system prompt•7 months ago
nft-standards
Implement NFT standards (ERC-721, ERC-1155) with proper metadata
coding
⭐1
# NFT Standards
Master ERC-721 and ERC-1155 NFT standards, metadata best practices, and advanced NFT features.
## When to Use This Skill
- Creating NFT collections (art, gaming, collectibles)
- Implementing marketplace functionality
- Building on-chain or off-chain metadata
- Creating soulbound tokens (non-transferable)
- Implementing royalties and revenue sharing
- Developing dynamic/evolving NFTs
## ERC-721 (Non-Fungible Token Standard)
```solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721Enumerable.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/utils/Counters.sol";
contract MyNFT is ERC721URIStorage, ERC721Enumerable, Ownable {
using Counters for Counters.Counter;
Counters.Counter private _tokenIds;
uint256 public constant MAX_SUPPLY = 10000;
uint256 public constant MINT_PRICE = 0.08 ether;
uint256 public constant MAX_PER_MINT = 20;
constructor() ERC721("MyNFT", "MNFT") {}
function mint(uint256 quantity) external payable {
require(quantity > 0 && quantity <= MAX_PER_MINT, "Invalid quantity");
require(_tokenIds.current() + quantity <= MAX_SUPPLY, "Exceeds max supply");
require(msg.value >= MINT_PRICE * quantity, "Insufficient payment");
for (uint256 i = 0; i < quantity; i++) {
_tokenIds.increment();
uint256 newTokenId = _tokenIds.current();
_safeMint(msg.sender, newTokenId);
_setTokenURI(newTokenId, generateTokenURI(newTokenId));
}
}
function generateTokenURI(uint256 tokenId) internal pure returns (string memory) {
// Return IPFS URI or on-chain metadata
return string(abi.encodePacked("ipfs://QmHash/", Strings.toString(tokenId), ".json"));
}
// Required overrides
function _beforeTokenTransfer(
address from,
address to,
uint256 tokenId,
uint256 batchSize
) internal override(ERC721, ERC721Enumerable) {
super._beforeTokenTransfer(from, to, tokenId, batchSize);
}
function _burn(uint256 tokenId) internal override(ERC721, ERC721URIStorage) {
super._burn(tokenId);
}
function tokenURI(uint256 tokenId) public view override(ERC721, ERC721URIStorage) returns (string memory) {
return super.tokenURI(tokenId);
}
function supportsInterface(bytes4 interfaceId)
public
view
override(ERC721, ERC721Enumerable)
returns (bool)
{
return super.supportsInterface(interfaceId);
}
function withdraw() external onlyOwner {
payable(owner()).transfer(address(this).balance);
}
}
```
## ERC-1155 (Multi-Token Standard)
```solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "@openzeppelin/contracts/token/ERC1155/ERC1155.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
contract GameItems is ERC1155, Ownable {
uint256 public constant SWORD = 1;
uint256 public constant SHIELD = 2;
uint256 public constant POTION = 3;
mapping(uint256 => uint256) public tokenSupply;
mapping(uint256 => uint256) public maxSupply;
constructor() ERC1155("ipfs://QmBaseHash/{id}.json") {
maxSupply[SWORD] = 1000;
maxSupply[SHIELD] = 500;
maxSupply[POTION] = 10000;
}
function mint(
address to,
uint256 id,
uint256 amount
) external onlyOwner {
require(tokenSupply[id] + amount <= maxSupply[id], "Exceeds max supply");
_mint(to, id, amount, "");
tokenSupply[id] += amount;
}
function mintBatch(
address to,
uint256[] memory ids,
uint256[] memory amounts
) external onlyOwner {
for (uint256 i = 0; i < ids.length; i++) {
require(tokenSupply[ids[i]] + amounts[i] <= maxSupply[ids[i]], "Exceeds max supply");
tokenSupply[ids[i]] += amounts[i];
}
_mintBatch(to, ids, amounts, "");
}
function burn(
address from,
uint256 id,
uint256 amount
) external {
require(from == msg.sender || isApprovedForAll(from, msg.sender), "Not authorized");
_burn(from, id, amount);
tokenSupply[id] -= amount;
}
}
```
## Metadata Standards
### Off-Chain Metadata (IPFS)
```json
{
"name": "NFT #1",
"description": "Description of the NFT",
"image": "ipfs://QmImageHash",
"attributes": [
{
"trait_type": "Background",
"value": "Blue"
},
{
"trait_type": "Rarity",
"value": "Legendary"
},
{
"trait_type": "Power",
"value": 95,
"display_type": "number",
"max_value": 100
}
]
}
```
### On-Chain Metadata
```solidity
contract OnChainNFT is ERC721 {
struct Traits {
uint8 background;
uint8 body;
uint8 head;
uint8 rarity;
}
mapping(uint256 => Traits) public tokenTraits;
function tokenURI(uint256 tokenId) public view override returns (string memory) {
Traits memory traits = tokenTraits[tokenId];
string memory json = Base64.encode(
bytes(
string(
abi.encodePacked(
'{"name": "NFT #', Strings.toString(tokenId), '",',
'"description": "On-chain NFT",',
'"image": "data:image/svg+xml;base64,', generateSVG(traits), '",',
'"attributes": [',
'{"trait_type": "Background", "value": "', Strings.toString(traits.background), '"},',
'{"trait_type": "Rarity", "value": "', getRarityName(traits.rarity), '"}',
']}'
)
)
)
);
return string(abi.encodePacked("data:application/json;base64,", json));
}
function generateSVG(Traits memory traits) internal pure returns (string memory) {
// Generate SVG based on traits
return "...";
}
}
```
## Royalties (EIP-2981)
```solidity
import "@openzeppelin/contracts/interfaces/IERC2981.sol";
contract NFTWithRoyalties is ERC721, IERC2981 {
address public royaltyRecipient;
uint96 public royaltyFee = 500; // 5%
constructor() ERC721("Royalty NFT", "RNFT") {
royaltyRecipient = msg.sender;
}
function royaltyInfo(uint256 tokenId, uint256 salePrice)
external
view
override
returns (address receiver, uint256 royaltyAmount)
{
return (royaltyRecipient, (salePrice * royaltyFee) / 10000);
}
function setRoyalty(address recipient, uint96 fee) external onlyOwner {
require(fee <= 1000, "Royalty fee too high"); // Max 10%
royaltyRecipient = recipient;
royaltyFee = fee;
}
function supportsInterface(bytes4 interfaceId)
public
view
override(ERC721, IERC165)
returns (bool)
{
return interfaceId == type(IERC2981).interfaceId ||
super.supportsInterface(interfaceId);
}
}
```
## Soulbound Tokens (Non-Transferable)
```solidity
contract SoulboundToken is ERC721 {
constructor() ERC721("Soulbound", "SBT") {}
function _beforeTokenTransfer(
address from,
address to,
uint256 tokenId,
uint256 batchSize
) internal virtual override {
require(from == address(0) || to == address(0), "Token is soulbound");
super._beforeTokenTransfer(from, to, tokenId, batchSize);
}
function mint(address to) external {
uint256 tokenId = totalSupply() + 1;
_safeMint(to, tokenId);
}
// Burn is allowed (user can destroy their SBT)
function burn(uint256 tokenId) external {
require(ownerOf(tokenId) == msg.sender, "Not token owner");
_burn(tokenId);
}
}
```
## Dynamic NFTs
```solidity
contract DynamicNFT is ERC721 {
struct TokenState {
uint256 level;
uint256 experience;
uint256 lastUpdated;
}
mapping(uint256 => TokenState) public tokenStates;
function gainExperience(uint256 tokenId, uint256 exp) external {
require(ownerOf(tokenId) == msg.sender, "Not token owner");
TokenState storage state = tokenStates[tokenId];
state.experience += exp;
// Level up logic
if (state.experience >= state.level * 100) {
state.level++;
}
state.lastUpdated = block.timestamp;
}
function tokenURI(uint256 tokenId) public view override returns (string memory) {
TokenState memory state = tokenStates[tokenId];
// Generate metadata based on current state
return generateMetadata(tokenId, state);
}
function generateMetadata(uint256 tokenId, TokenState memory state)
internal
pure
returns (string memory)
{
// Dynamic metadata generation
return "";
}
}
```
## Gas-Optimized Minting (ERC721A)
```solidity
import "erc721a/contracts/ERC721A.sol";
contract OptimizedNFT is ERC721A {
uint256 public constant MAX_SUPPLY = 10000;
uint256 public constant MINT_PRICE = 0.05 ether;
constructor() ERC721A("Optimized NFT", "ONFT") {}
function mint(uint256 quantity) external payable {
require(_totalMinted() + quantity <= MAX_SUPPLY, "Exceeds max supply");
require(msg.value >= MINT_PRICE * quantity, "Insufficient payment");
_mint(msg.sender, quantity);
}
function _baseURI() internal pure override returns (string memory) {
return "ipfs://QmBaseHash/";
}
}
```
## Resources
- **references/erc721.md**: ERC-721 specification details
- **references/erc1155.md**: ERC-1155 multi-token standard
- **references/metadata-standards.md**: Metadata best practices
- **references/enumeration.md**: Token enumeration patterns
- **assets/erc721-contract.sol**: Production ERC-721 template
- **assets/erc1155-contract.sol**: Production ERC-1155 template
- **assets/metadata-schema.json**: Standard metadata format
- **assets/metadata-uploader.py**: IPFS upload utility
## Best Practices
1. **Use OpenZeppelin**: Battle-tested implementations
2. **Pin Metadata**: Use IPFS with pinning service
3. **Implement Royalties**: EIP-2981 for marketplace compatibility
4. **Gas Optimization**: Use ERC721A for batch minting
5. **Reveal Mechanism**: Placeholder → reveal pattern
6. **Enumeration**: Support walletOfOwner for marketplaces
7. **Whitelist**: Merkle trees for efficient whitelisting
## Marketplace Integration
- OpenSea: ERC-721/1155, metadata standards
- LooksRare: Royalty enforcement
- Rarible: Protocol fees, lazy minting
- Blur: Gas-optimized trading
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