Token Standards

Token Standards

ERC-20 (Fungible Tokens)

Use for: Currency, utility tokens, governance tokens, stablecoins, LP tokens

Core Interface

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function transfer(address to, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address from, address to, uint256 amount) external returns (bool);
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

Extensions

• ERC-20Permit (EIP-2612): Gasless approvals via EIP-712 signatures. User signs off-chain, protocol submits permit + transferFrom in one tx.
• ERC-20Votes: Snapshot-based voting power. Checkpoints at every transfer. Required for governance.
• ERC-20Burnable: burn(amount) and burnFrom(account, amount).
• ERC-20Capped: Max supply enforced in _mint().
• ERC-20Pausable: Owner can pause all transfers (emergency stop).

Gotchas — Non-Standard Tokens

ALWAYS use OpenZeppelin's SafeERC20 for external token interactions.

ERC-721 (Non-Fungible Tokens)

Use for: Unique digital assets, NFT collections, deeds, certificates

Core Interface

interface IERC721 {
    function balanceOf(address owner) external view returns (uint256);
    function ownerOf(uint256 tokenId) external view returns (address);
    function safeTransferFrom(address from, address to, uint256 tokenId) external;
    function transferFrom(address from, address to, uint256 tokenId) external;
    function approve(address to, uint256 tokenId) external;
    function setApprovalForAll(address operator, bool approved) external;
    function getApproved(uint256 tokenId) external view returns (address);
    function isApprovedForAll(address owner, address operator) external view returns (bool);
}

Extensions

• ERC721Metadata: name(), symbol(), tokenURI(uint256 tokenId)
• ERC721Enumerable: totalSupply(), tokenByIndex(), tokenOfOwnerByIndex() — expensive gas, avoid if not needed
• ERC721URIStorage: Per-token custom URI storage

Patterns

• Lazy minting: Don't mint on-chain until purchased. Save gas for unsold tokens.
• Merkle allowlists: Verify eligibility via Merkle proof instead of storing all addresses.
• Reveal: Mint with placeholder URI, reveal real metadata later via URI update.

ERC-1155 (Multi-Token)

Use for: Game items, prediction market outcome tokens, mixed fungible + non-fungible

Key Advantage

Single contract for multiple token types. Batch operations save gas.

interface IERC1155 {
    function balanceOf(address account, uint256 id) external view returns (uint256);
    function balanceOfBatch(address[] calldata accounts, uint256[] calldata ids) external view returns (uint256[] memory);
    function safeTransferFrom(address from, address to, uint256 id, uint256 amount, bytes calldata data) external;
    function safeBatchTransferFrom(address from, address to, uint256[] calldata ids, uint256[] calldata amounts, bytes calldata data) external;
    function setApprovalForAll(address operator, bool approved) external;
}

• Token ID determines type (fungible or unique based on supply)
• Perfect for prediction markets: each outcome is a token ID
• Gnosis Conditional Token Framework is built on ERC-1155

ERC-4626 (Tokenized Vaults)

Use for: Yield-bearing tokens, staking positions, any deposit→shares pattern

interface IERC4626 is IERC20 {
    function asset() external view returns (address);
    function totalAssets() external view returns (uint256);
    function deposit(uint256 assets, address receiver) external returns (uint256 shares);
    function withdraw(uint256 assets, address receiver, address owner) external returns (uint256 shares);
    function mint(uint256 shares, address receiver) external returns (uint256 assets);
    function redeem(uint256 shares, address receiver, address owner) external returns (uint256 assets);
    function convertToShares(uint256 assets) external view returns (uint256);
    function convertToAssets(uint256 shares) external view returns (uint256);
}

⚠️ CRITICAL: First Depositor / Inflation Attack

Attack: First depositor deposits 1 wei, then donates large amount to vault, inflating share price. Next depositor's shares round to 0. Prevention: Virtual shares/assets offset (OpenZeppelin 4.9+), or initial dead shares deposit by the protocol.

Other Key Standards

EIP-712 (Typed Structured Data Signing)

Standard for signing structured data off-chain. Used by Permit, meta-transactions, order books.

bytes32 constant DOMAIN_TYPEHASH = keccak256(
    "EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"
);

EIP-4337 (Account Abstraction)

Smart contract wallets with UserOperations, Bundlers, EntryPoint, Paymasters. See account-abstraction skill.

EIP-1167 (Minimal Proxy / Clones)

Deploy cheap copies of a contract. ~45 bytes of bytecode, delegates all calls to implementation.

EIP-2535 (Diamond Standard)

Multiple implementation contracts (facets) behind one proxy. Function selector → facet routing.

EIP-7702 (Set EOA Code)

Allows EOAs to temporarily adopt smart contract code. Bridges EOA and smart wallet worlds.

EIP-5192 (Soulbound Tokens)

Non-transferable tokens. locked(uint256 tokenId) returns true if token can't be transferred.

ERC-2981 (Royalty Standard)

function royaltyInfo(uint256 tokenId, uint256 salePrice) external view returns (address receiver, uint256 royaltyAmount);

Standard way to signal royalty info. Not enforced on-chain by default — requires marketplace cooperation or transfer hooks.