> ## Documentation Index > Fetch the complete documentation index at: https://docs.immutable.com/llms.txt > Use this file to discover all available pages before exploring further. # ERC-20 (In-Game Currencies) ERC-20 tokens are fungible—each unit is identical and interchangeable. Use them for in-game currencies, reward points, governance tokens, or any divisible asset. ## Why Use ERC-20? Players own their currency on-chain. They keep it even if they stop playing your game. List on DEXes or enable peer-to-peer trading. Players can buy/sell currency with real market prices. Same token can work across multiple games. Build partnerships and shared economies. All supply, distribution, and transactions are verifiable on-chain. Players trust what they can verify. ## Deploy via Hub Deploy ERC-20 contracts in Hub ## Deploy via Code ```solidity theme={null} // SPDX-License-Identifier: MIT pragma solidity ^0.8.19; import "@openzeppelin/contracts/token/ERC20/ERC20.sol"; import "@openzeppelin/contracts/access/Ownable.sol"; contract GameCurrency is ERC20, Ownable { constructor() ERC20("Gold Coins", "GOLD") Ownable(msg.sender) { _mint(msg.sender, 1000000 * 10 ** decimals()); } function mint(address to, uint256 amount) external onlyOwner { _mint(to, amount); } } ``` ## Distribution Patterns ### Achievement Rewards ```typescript theme={null} const REWARDS = { 'first_kill': 100n * 10n ** 18n, 'level_10': 500n * 10n ** 18n, 'boss_defeated': 1000n * 10n ** 18n, }; async function grantAchievement(player: string, achievement: string) { const reward = REWARDS[achievement]; if (reward) await currencyContract.mint(player, reward); } ``` ### Daily Login ```typescript theme={null} async function claimDailyReward(player: string) { const lastClaim = await getLastClaimTime(player); if (Date.now() - lastClaim < 24 * 60 * 60 * 1000) { throw new Error('Already claimed today'); } await currencyContract.mint(player, 50n * 10n ** 18n); await setLastClaimTime(player, Date.now()); } ``` ## Spending Currency ### In-Game Purchases ```typescript theme={null} async function purchaseItem(player: string, itemId: string, price: bigint) { // Transfer from player to treasury await currencyContract.transferFrom(player, TREASURY, price); // Grant the item await grantItem(player, itemId); } ``` ### Approval Flow Players must approve your contract to spend their tokens: ```typescript theme={null} // Frontend: Request approval async function approveSpending(amount: bigint) { const signer = await ethersProvider.getSigner(); const currency = new ethers.Contract(CURRENCY_ADDRESS, ERC20_ABI, signer); await currency.approve(GAME_CONTRACT, amount); } ``` ## Balance Queries ```typescript theme={null} // Direct contract call const balance = await currencyContract.balanceOf(playerAddress); console.log(`${ethers.formatEther(balance)} GOLD`); // Via Indexer API const tokens = await indexer.listTokensByAccountAddress({ chainName: 'imtbl-zkevm-mainnet', accountAddress: playerAddress, }); ``` See [Indexer API](/docs/products/indexer/overview) for querying token balances. ## Economy Design * Set maximum supply caps * Implement burning mechanics (consumables, fees) * Balance earn rates with spending sinks * **Soft currency**: Earned through gameplay, unlimited * **Hard currency**: Purchased or rare, limited supply * **Seasonal currency**: Resets each season * Rate limit claims per wallet * Require game actions, not just API calls * Monitor for suspicious patterns ## Next Steps Deploy via Hub Query token balances Explore other contract types Deploy programmatically