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skills/aave/SKILL.md

Aave V3

Aave V3 is the dominant on-chain lending protocol. Users supply assets to earn yield and borrow against collateral. The protocol runs on Ethereum, Arbitrum, Optimism, Base, Polygon, and other EVM chains with identical interfaces. All interaction goes through the IPool contract.

What You Probably Got Wrong

LLMs confuse V2 and V3 constantly. V3 has different interfaces, different addresses, and different behavior. These corrections are non-negotiable.

V3 is not V2 — different interfaces everywhere — V2 uses LendingPool with deposit(). V3 uses Pool with supply(). The function signatures, events, and return types differ. If you see ILendingPool or deposit(), you are writing V2 code. Stop.
aTokens rebase — balance changes every block — aToken.balanceOf(user) increases each block as interest accrues. This is not a transfer. Do not try to track balances with Transfer events alone. Use balanceOf() at read time or scaledBalanceOf() for the underlying non-rebasing amount.
Stable rate borrowing is deprecated on most markets — Aave governance disabled stable rate borrows on Ethereum mainnet and most L2 deployments. Use VARIABLE_RATE = 2 for the interestRateMode parameter. Passing STABLE_RATE = 1 will revert on markets where it is disabled.
Health factor is 18-decimal fixed point, not a percentage — getUserAccountData() returns healthFactor as a uint256 with 18 decimals. A health factor of 1e18 means liquidation threshold. Below 1e18 = liquidatable. Do not divide by 100.
Flash loan fee is 0.05% on V3, not 0.09% — V3 reduced the default flash loan premium from 0.09% (V2) to 0.05%. The exact fee is configurable per market via governance. Check FLASHLOAN_PREMIUM_TOTAL on the Pool contract.
E-Mode changes collateral/borrow parameters — Enabling E-Mode (Efficiency Mode) overrides LTV, liquidation threshold, and liquidation bonus for assets in the same category (e.g., stablecoins). It does NOT change the underlying asset. Forgetting this causes incorrect health factor calculations.
Supply caps exist in V3 — V3 introduced per-asset supply and borrow caps. supply() will revert if the cap is reached. Always check getReserveData() for supplyCap before large deposits.
V3 addresses are different per chain AND per market — Ethereum has a "Main" market and a "Lido" market with completely different Pool addresses. Always verify you are targeting the correct market.

Quick Start

Installation

npm install @aave/aave-v3-core viem

For TypeScript projects, the @aave/aave-v3-core package provides Solidity interfaces. For frontend/backend interaction, use viem directly with the ABIs below.

Minimal ABI Fragments

const poolAbi = [
  {
    name: "supply",
    type: "function",
    stateMutability: "nonpayable",
    inputs: [
      { name: "asset", type: "address" },
      { name: "amount", type: "uint256" },
      { name: "onBehalfOf", type: "address" },
      { name: "referralCode", type: "uint16" },
    ],
    outputs: [],
  },
  {
    name: "borrow",
    type: "function",
    stateMutability: "nonpayable",
    inputs: [
      { name: "asset", type: "address" },
      { name: "amount", type: "uint256" },
      { name: "interestRateMode", type: "uint256" },
      { name: "referralCode", type: "uint16" },
      { name: "onBehalfOf", type: "address" },
    ],
    outputs: [],
  },
  {
    name: "repay",
    type: "function",
    stateMutability: "nonpayable",
    inputs: [
      { name: "asset", type: "address" },
      { name: "amount", type: "uint256" },
      { name: "interestRateMode", type: "uint256" },
      { name: "onBehalfOf", type: "address" },
    ],
    outputs: [{ name: "", type: "uint256" }],
  },
  {
    name: "withdraw",
    type: "function",
    stateMutability: "nonpayable",
    inputs: [
      { name: "asset", type: "address" },
      { name: "amount", type: "uint256" },
      { name: "to", type: "address" },
    ],
    outputs: [{ name: "", type: "uint256" }],
  },
  {
    name: "getUserAccountData",
    type: "function",
    stateMutability: "view",
    inputs: [{ name: "user", type: "address" }],
    outputs: [
      { name: "totalCollateralBase", type: "uint256" },
      { name: "totalDebtBase", type: "uint256" },
      { name: "availableBorrowsBase", type: "uint256" },
      { name: "currentLiquidationThreshold", type: "uint256" },
      { name: "ltv", type: "uint256" },
      { name: "healthFactor", type: "uint256" },
    ],
  },
  {
    name: "flashLoanSimple",
    type: "function",
    stateMutability: "nonpayable",
    inputs: [
      { name: "receiverAddress", type: "address" },
      { name: "asset", type: "address" },
      { name: "amount", type: "uint256" },
      { name: "params", type: "bytes" },
      { name: "referralCode", type: "uint16" },
    ],
    outputs: [],
  },
  {
    name: "setUserEMode",
    type: "function",
    stateMutability: "nonpayable",
    inputs: [{ name: "categoryId", type: "uint8" }],
    outputs: [],
  },
  {
    name: "getReserveData",
    type: "function",
    stateMutability: "view",
    inputs: [{ name: "asset", type: "address" }],
    outputs: [
      {
        name: "",
        type: "tuple",
        components: [
          { name: "configuration", type: "uint256" },
          { name: "liquidityIndex", type: "uint128" },
          { name: "currentLiquidityRate", type: "uint128" },
          { name: "variableBorrowIndex", type: "uint128" },
          { name: "currentVariableBorrowRate", type: "uint128" },
          { name: "currentStableBorrowRate", type: "uint128" },
          { name: "lastUpdateTimestamp", type: "uint40" },
          { name: "id", type: "uint16" },
          { name: "aTokenAddress", type: "address" },
          { name: "stableDebtTokenAddress", type: "address" },
          { name: "variableDebtTokenAddress", type: "address" },
          { name: "interestRateStrategyAddress", type: "address" },
          { name: "accruedToTreasury", type: "uint128" },
          { name: "unbacked", type: "uint128" },
          { name: "isolationModeTotalDebt", type: "uint128" },
        ],
      },
    ],
  },
] as const;

const erc20Abi = [
  {
    name: "approve",
    type: "function",
    stateMutability: "nonpayable",
    inputs: [
      { name: "spender", type: "address" },
      { name: "amount", type: "uint256" },
    ],
    outputs: [{ name: "", type: "bool" }],
  },
  {
    name: "balanceOf",
    type: "function",
    stateMutability: "view",
    inputs: [{ name: "account", type: "address" }],
    outputs: [{ name: "", type: "uint256" }],
  },
] as const;

Basic Supply (TypeScript)

import { createPublicClient, createWalletClient, http, parseUnits } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { mainnet } from "viem/chains";

const POOL = "0x87870Bca3F3fD6335C3F4ce8392D69350B4fA4E2" as const;
const USDC = "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48" as const;

const account = privateKeyToAccount(process.env.PRIVATE_KEY as `0x${string}`);

const publicClient = createPublicClient({
  chain: mainnet,
  transport: http(process.env.RPC_URL),
});

const walletClient = createWalletClient({
  account,
  chain: mainnet,
  transport: http(process.env.RPC_URL),
});

const amount = parseUnits("1000", 6); // 1000 USDC

// Approve Pool to spend USDC
const approveHash = await walletClient.writeContract({
  address: USDC,
  abi: erc20Abi,
  functionName: "approve",
  args: [POOL, amount],
});
await publicClient.waitForTransactionReceipt({ hash: approveHash });

// Supply USDC to Aave
const supplyHash = await walletClient.writeContract({
  address: POOL,
  abi: poolAbi,
  functionName: "supply",
  args: [USDC, amount, account.address, 0],
});
const receipt = await publicClient.waitForTransactionReceipt({ hash: supplyHash });

if (receipt.status !== "success") {
  throw new Error("Supply transaction reverted");
}

Core Operations

Supply (Solidity)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import {IPool} from "@aave/aave-v3-core/contracts/interfaces/IPool.sol";
import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract AaveSupplier {
    IPool public immutable pool;

    constructor(address _pool) {
        pool = IPool(_pool);
    }

    /// @notice Supply asset to Aave V3 on behalf of msg.sender
    /// @param asset ERC20 token to supply
    /// @param amount Amount in token's native decimals
    function supplyToAave(address asset, uint256 amount) external {
        IERC20(asset).transferFrom(msg.sender, address(this), amount);
        IERC20(asset).approve(address(pool), amount);
        pool.supply(asset, amount, msg.sender, 0);
    }
}

Borrow (TypeScript)

// Variable rate = 2. Stable rate (1) is deprecated on most markets.
const VARIABLE_RATE = 2n;

const borrowHash = await walletClient.writeContract({
  address: POOL,
  abi: poolAbi,
  functionName: "borrow",
  args: [USDC, parseUnits("500", 6), VARIABLE_RATE, 0, account.address],
});
const borrowReceipt = await publicClient.waitForTransactionReceipt({ hash: borrowHash });

if (borrowReceipt.status !== "success") {
  throw new Error("Borrow transaction reverted");
}

Repay (TypeScript)

const repayAmount = parseUnits("500", 6);

// Approve Pool to pull repayment
const repayApproveHash = await walletClient.writeContract({
  address: USDC,
  abi: erc20Abi,
  functionName: "approve",
  args: [POOL, repayAmount],
});
await publicClient.waitForTransactionReceipt({ hash: repayApproveHash });

// type(uint256).max to repay entire debt
const repayHash = await walletClient.writeContract({
  address: POOL,
  abi: poolAbi,
  functionName: "repay",
  args: [USDC, repayAmount, 2n, account.address],
});
const repayReceipt = await publicClient.waitForTransactionReceipt({ hash: repayHash });

if (repayReceipt.status !== "success") {
  throw new Error("Repay transaction reverted");
}

Withdraw (TypeScript)

// type(uint256).max withdraws entire balance
const maxUint256 = 2n ** 256n - 1n;

const withdrawHash = await walletClient.writeContract({
  address: POOL,
  abi: poolAbi,
  functionName: "withdraw",
  args: [USDC, maxUint256, account.address],
});
const withdrawReceipt = await publicClient.waitForTransactionReceipt({
  hash: withdrawHash,
});

if (withdrawReceipt.status !== "success") {
  throw new Error("Withdraw transaction reverted");
}

Repay and Withdraw (Solidity)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import {IPool} from "@aave/aave-v3-core/contracts/interfaces/IPool.sol";
import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract AavePositionManager {
    IPool public immutable pool;

    constructor(address _pool) {
        pool = IPool(_pool);
    }

    /// @notice Repay variable-rate debt on behalf of msg.sender
    function repayDebt(address asset, uint256 amount) external {
        IERC20(asset).transferFrom(msg.sender, address(this), amount);
        IERC20(asset).approve(address(pool), amount);
        // interestRateMode 2 = variable rate
        pool.repay(asset, amount, 2, msg.sender);
    }

    /// @notice Withdraw supplied asset back to msg.sender
    /// @param amount Use type(uint256).max to withdraw entire balance
    function withdrawFromAave(address asset, uint256 amount) external {
        pool.withdraw(asset, amount, msg.sender);
    }
}

Flash Loans

V3 provides flashLoanSimple for single-asset flash loans (simpler interface, lower gas) and flashLoan for multi-asset. The fee is 0.05% by default.

Flash Loan Receiver (Solidity)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import {IPool} from "@aave/aave-v3-core/contracts/interfaces/IPool.sol";
import {IFlashLoanSimpleReceiver} from
    "@aave/aave-v3-core/contracts/flashloan/base/FlashLoanSimpleReceiver.sol";
import {IPoolAddressesProvider} from
    "@aave/aave-v3-core/contracts/interfaces/IPoolAddressesProvider.sol";
import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract SimpleFlashLoan is IFlashLoanSimpleReceiver {
    IPoolAddressesProvider public immutable override ADDRESSES_PROVIDER;
    IPool public immutable override POOL;

    constructor(address provider) {
        ADDRESSES_PROVIDER = IPoolAddressesProvider(provider);
        POOL = IPool(IPoolAddressesProvider(provider).getPool());
    }

    /// @notice Called by Aave Pool after flash loan funds are transferred
    /// @dev Must approve Pool to pull back (amount + premium) before returning
    function executeOperation(
        address asset,
        uint256 amount,
        uint256 premium,
        address initiator,
        bytes calldata /* params */
    ) external override returns (bool) {
        if (msg.sender != address(POOL)) revert("Caller not Pool");
        if (initiator != address(this)) revert("Initiator not this contract");

        // --- Custom logic here ---
        // You have `amount` of `asset` available in this contract.
        // Do arbitrage, liquidation, collateral swap, etc.

        // Repay flash loan: approve Pool to pull amount + fee
        uint256 amountOwed = amount + premium;
        IERC20(asset).approve(address(POOL), amountOwed);

        return true;
    }

    /// @notice Trigger a flash loan
    /// @param asset Token to borrow
    /// @param amount Amount to flash borrow
    function requestFlashLoan(address asset, uint256 amount) external {
        POOL.flashLoanSimple(address(this), asset, amount, "", 0);
    }
}

Trigger Flash Loan (TypeScript)

const flashLoanContractAddress = "0x...YOUR_DEPLOYED_CONTRACT..." as `0x${string}`;

const flashLoanAbi = [
  {
    name: "requestFlashLoan",
    type: "function",
    stateMutability: "nonpayable",
    inputs: [
      { name: "asset", type: "address" },
      { name: "amount", type: "uint256" },
    ],
    outputs: [],
  },
] as const;

// Flash borrow 1M USDC
const txHash = await walletClient.writeContract({
  address: flashLoanContractAddress,
  abi: flashLoanAbi,
  functionName: "requestFlashLoan",
  args: [USDC, parseUnits("1000000", 6)],
});

const flashReceipt = await publicClient.waitForTransactionReceipt({ hash: txHash });

if (flashReceipt.status !== "success") {
  throw new Error("Flash loan reverted");
}

Reading Protocol State

Get User Account Data

const [
  totalCollateralBase,
  totalDebtBase,
  availableBorrowsBase,
  currentLiquidationThreshold,
  ltv,
  healthFactor,
] = await publicClient.readContract({
  address: POOL,
  abi: poolAbi,
  functionName: "getUserAccountData",
  args: [account.address],
});

// All "Base" values are in USD with 8 decimals (Aave oracle base currency)
const collateralUsd = Number(totalCollateralBase) / 1e8;
const debtUsd = Number(totalDebtBase) / 1e8;

// healthFactor has 18 decimals. Below 1e18 = liquidatable.
const hf = Number(healthFactor) / 1e18;
console.log(`Health Factor: ${hf}`);
console.log(`Collateral: $${collateralUsd}, Debt: $${debtUsd}`);

Get Reserve Data

const reserveData = await publicClient.readContract({
  address: POOL,
  abi: poolAbi,
  functionName: "getReserveData",
  args: [USDC],
});

// Supply APY: currentLiquidityRate is a ray (27 decimals)
const supplyRateRay = reserveData.currentLiquidityRate;
const supplyAPY = Number(supplyRateRay) / 1e27;
console.log(`USDC Supply APY: ${(supplyAPY * 100).toFixed(2)}%`);

// aToken address for this reserve
const aTokenAddress = reserveData.aTokenAddress;

Track aToken Balance

// aToken balance includes accrued interest (rebases every block)
const aUsdcBalance = await publicClient.readContract({
  address: reserveData.aTokenAddress,
  abi: erc20Abi,
  functionName: "balanceOf",
  args: [account.address],
});

// Balance in human-readable format (USDC has 6 decimals)
const balanceFormatted = Number(aUsdcBalance) / 1e6;
console.log(`aUSDC balance: ${balanceFormatted}`);

Contract Addresses

Last verified: 2025-05-01

All Aave V3 deployments share the same interface. Addresses sourced from @bgd-labs/aave-address-book and official Aave governance.

Pool (main entry point for all operations)

Chain	Address
Ethereum	`0x87870Bca3F3fD6335C3F4ce8392D69350B4fA4E2`
Arbitrum	`0x794a61358D6845594F94dc1DB02A252b5b4814aD`
Optimism	`0x794a61358D6845594F94dc1DB02A252b5b4814aD`
Polygon	`0x794a61358D6845594F94dc1DB02A252b5b4814aD`
Base	`0xA238Dd80C259a72e81d7e4664a9801593F98d1c5`

PoolAddressesProvider

Chain	Address
Ethereum	`0x2f39d218133AFaB8F2B819B1066c7E434Ad94E9e`
Arbitrum	`0xa97684ead0e402dC232d5A977953DF7ECBaB3CDb`
Optimism	`0xa97684ead0e402dC232d5A977953DF7ECBaB3CDb`
Polygon	`0xa97684ead0e402dC232d5A977953DF7ECBaB3CDb`
Base	`0xe20fCBdBfFC4Dd138cE8b2E6FBb6CB49777ad64D`

Aave Oracle

Chain	Address
Ethereum	`0x54586bE62E3c3580375aE3723C145253060Ca0C2`
Arbitrum	`0xb56c2F0B653B2e0b10C9b928C8580Ac5Df02C7C7`
Optimism	`0xD81eb3728a631871a7eBBaD631b5f424909f0c77`
Polygon	`0xb023e699F5a33916Ea823A16485e259257cA8Bd1`
Base	`0x2Cc0Fc26eD4563A5ce5e8bdcfe1A2878676Ae156`

Common Token Addresses (Ethereum Mainnet)

Token	Address
WETH	`0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2`
USDC	`0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48`
USDT	`0xdAC17F958D2ee523a2206206994597C13D831ec7`
DAI	`0x6B175474E89094C44Da98b954EedeAC495271d0F`
WBTC	`0x2260FAC5E5542a773Aa44fBCfeDf7C193bc2C599`

Verify any address before mainnet use: cast code <address> --rpc-url $RPC_URL

E-Mode (Efficiency Mode)

E-Mode lets users achieve higher capital efficiency when borrowing and supplying correlated assets (e.g., stablecoins against stablecoins, ETH against stETH).

How It Works

Each E-Mode category defines:

Higher LTV (e.g., 97% for stablecoins vs 75% default)
Higher liquidation threshold (e.g., 97.5%)
Lower liquidation bonus (e.g., 1% vs 5%)
Optional oracle override for the category

Common E-Mode Categories

ID	Label	Typical LTV	Use Case
0	None (default)	Varies per asset	General lending
1	Stablecoins	97%	Borrow USDT against USDC
2	ETH correlated	93%	Borrow WETH against wstETH

Category IDs and parameters vary by chain and market. Query on-chain.

Enable E-Mode (TypeScript)

// Enable stablecoin E-Mode (category 1)
const emodeHash = await walletClient.writeContract({
  address: POOL,
  abi: poolAbi,
  functionName: "setUserEMode",
  args: [1],
});
await publicClient.waitForTransactionReceipt({ hash: emodeHash });

Enable E-Mode (Solidity)

// Enable E-Mode before supplying/borrowing for higher LTV
pool.setUserEMode(1); // 1 = stablecoins category

// To disable, set back to 0
// Reverts if current position would be undercollateralized without E-Mode
pool.setUserEMode(0);

E-Mode Constraint

You can only borrow assets that belong to the active E-Mode category. Supplying is unrestricted. Setting E-Mode to 0 reverts if your position would become unhealthy at default LTV/threshold.

Error Handling

Error Code	Name	Cause	Fix
1	`CALLER_NOT_POOL_ADMIN`	Non-admin calling admin function	Use correct admin account
26	`COLLATERAL_CANNOT_COVER_NEW_BORROW`	Insufficient collateral for borrow	Supply more collateral or borrow less
27	`COLLATERAL_SAME_AS_BORROWING_CURRENCY`	Cannot use same asset as collateral and borrow in isolation mode	Use a different collateral
28	`AMOUNT_BIGGER_THAN_MAX_LOAN_SIZE_STABLE`	Stable rate borrow exceeds limit	Use variable rate (`interestRateMode = 2`)
29	`NO_DEBT_OF_SELECTED_TYPE`	Repaying debt type that does not exist	Check `interestRateMode` matches your debt
30	`NO_EXPLICIT_AMOUNT_TO_REPAY_ON_BEHALF`	Repaying on behalf with `type(uint256).max`	Specify exact repay amount when paying for another user
35	`HEALTH_FACTOR_LOWER_THAN_LIQUIDATION_THRESHOLD`	Action would make position liquidatable	Reduce borrow amount or add collateral
36	`INCONSISTENT_EMODE_CATEGORY`	Borrowing asset outside active E-Mode category	Switch E-Mode or borrow a compatible asset
50	`SUPPLY_CAP_EXCEEDED`	Asset supply cap reached	Wait for withdrawals or use a different market
51	`BORROW_CAP_EXCEEDED`	Asset borrow cap reached	Wait for repayments or use a different market

Full error code list: contracts/protocol/libraries/helpers/Errors.sol in aave-v3-core

Handling Reverts in TypeScript

import { BaseError, ContractFunctionRevertedError } from "viem";

try {
  await publicClient.simulateContract({
    address: POOL,
    abi: poolAbi,
    functionName: "borrow",
    args: [USDC, parseUnits("500", 6), 2n, 0, account.address],
    account: account.address,
  });
} catch (err) {
  if (err instanceof BaseError) {
    const revertError = err.walk(
      (e) => e instanceof ContractFunctionRevertedError
    );
    if (revertError instanceof ContractFunctionRevertedError) {
      const errorName = revertError.data?.errorName;
      console.error(`Aave revert: ${errorName}`);
    }
  }
}

Security

Health Factor Monitoring

A health factor below 1.0 means the position is liquidatable. Third-party liquidators actively monitor the mempool. Always maintain a buffer.

async function checkHealthFactor(
  userAddress: `0x${string}`
): Promise<{ safe: boolean; healthFactor: number }> {
  const [, , , , , healthFactor] = await publicClient.readContract({
    address: POOL,
    abi: poolAbi,
    functionName: "getUserAccountData",
    args: [userAddress],
  });

  const hf = Number(healthFactor) / 1e18;

  // 1.5 is a conservative safety buffer
  return { safe: hf > 1.5, healthFactor: hf };
}

Liquidation Risk Factors

Oracle price movement — If collateral price drops or debt price increases, health factor drops. Aave uses Chainlink oracles; check feed freshness.
Accruing interest — Variable borrow rates compound. A 50% APY borrow accumulates debt faster than most users expect.
E-Mode exit — Disabling E-Mode instantly applies lower LTV/thresholds. A safe E-Mode position may become liquidatable at default parameters.
Supply cap filling — If you need to add emergency collateral and the supply cap is full, you cannot. Diversify collateral types.

Best Practices

Simulate before executing — Always call simulateContract before writeContract to catch reverts without spending gas.
Check receipt.status — A confirmed transaction can still revert. Always verify receipt.status === "success".
Monitor health factor off-chain — Set up alerts when HF drops below 2.0. Automate repayment or collateral addition below 1.5.
Never hardcode gas limits for Aave calls — Pool operations have variable gas costs depending on reserves touched, E-Mode state, and isolation mode. Let the node estimate.
Approve exact amounts — Avoid type(uint256).max approvals in production. Approve only what is needed per transaction.

References

optimism

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Author

@0xinit

Stars

Repository

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skills/optimism/SKILL.md

Optimism

Optimism is an EVM-equivalent Layer 2 using optimistic rollups. Transactions execute on L2 with data posted to Ethereum L1 for security. The OP Stack is the modular framework powering OP Mainnet, Base, Zora, Mode, and the broader Superchain. Smart contracts deploy identically to Ethereum — no custom compiler, no special opcodes.

What You Probably Got Wrong

OP Mainnet IS EVM-equivalent, not just EVM-compatible — Your Solidity contracts deploy without modification. No --legacy flag, no custom compiler. forge create and hardhat deploy work identically to Ethereum. If someone tells you to change your Solidity for "OP compatibility", they are wrong.
Gas has two components, not one — Every transaction pays L2 execution gas AND an L1 data fee for posting calldata/blobs to Ethereum. If you only estimate L2 gas via eth_estimateGas, your cost estimate will be wrong. The L1 data fee often dominates total cost. Use the GasPriceOracle predeploy at 0x420000000000000000000000000000000000000F.
L2→L1 withdrawals take 7 days, not minutes — L1→L2 deposits finalize in ~1-3 minutes. L2→L1 withdrawals require a 7-day challenge period (the "fault proof window"). Users must prove the withdrawal, wait 7 days, then finalize. Three separate transactions on L1. If your UX assumes instant bridging both ways, it is broken.
block.number returns the L2 block number, not L1 — On OP Mainnet, block.number is the L2 block number. To get the L1 block number, read the L1Block predeploy at 0x4200000000000000000000000000000000000015. L2 blocks are produced every 2 seconds.
msg.sender works normally — there is no tx.origin aliasing on L2 — Cross-domain messages from L1 to L2 alias the sender address (add 0x1111000000000000000000000000000000001111). But for normal L2 transactions, msg.sender behaves exactly like Ethereum. Only worry about aliasing when receiving L1→L2 messages in your contract.
Predeploy contracts live at fixed addresses starting with 0x4200... — These are NOT deployed by you. They exist at genesis. L2CrossDomainMessenger, L2StandardBridge, GasPriceOracle, L1Block, and others all live at hardcoded addresses in the 0x4200... range. Do not try to deploy them.
The sequencer is centralized but cannot steal funds — The sequencer orders transactions and proposes state roots. If it goes down, you cannot submit new transactions until it recovers (or until permissionless fault proofs allow forced inclusion). But the sequencer cannot forge invalid state — the fault proof system protects withdrawals.
EIP-4844 blob data changed the gas model — After the Ecotone upgrade (March 2024), OP Mainnet posts data using EIP-4844 blobs instead of calldata. This reduced L1 data fees by ~10-100x. The GasPriceOracle methods changed. If you are reading pre-Ecotone documentation, the fee formulas are outdated.
SuperchainERC20 is not a standard ERC20 — It is a cross-chain token standard for OP Stack chains that enables native interop between Superchain members. Tokens must implement ICrosschainERC20 with crosschainMint and crosschainBurn. Do not assume a regular ERC20 works across chains.

Quick Start

Chain Configuration

import { defineChain } from "viem";
import { optimism, optimismSepolia } from "viem/chains";

// OP Mainnet is built-in
// Chain ID: 10
// RPC: https://mainnet.optimism.io
// Explorer: https://optimistic.etherscan.io

// OP Sepolia is also built-in
// Chain ID: 11155420
// RPC: https://sepolia.optimism.io
// Explorer: https://sepolia-optimistic.etherscan.io

Environment Setup

# .env
PRIVATE_KEY=your_private_key_here
OP_MAINNET_RPC=https://mainnet.optimism.io
OP_SEPOLIA_RPC=https://sepolia.optimism.io
ETHERSCAN_API_KEY=your_optimistic_etherscan_api_key

Viem Client Setup

import { createPublicClient, createWalletClient, http } from "viem";
import { optimism } from "viem/chains";
import { privateKeyToAccount } from "viem/accounts";

const account = privateKeyToAccount(`0x${process.env.PRIVATE_KEY}`);

const publicClient = createPublicClient({
  chain: optimism,
  transport: http(process.env.OP_MAINNET_RPC),
});

const walletClient = createWalletClient({
  account,
  chain: optimism,
  transport: http(process.env.OP_MAINNET_RPC),
});

Chain Configuration

Property	OP Mainnet	OP Sepolia
Chain ID	10	11155420
Currency	ETH	ETH
RPC	`https://mainnet.optimism.io`	`https://sepolia.optimism.io`
Explorer	`https://optimistic.etherscan.io`	`https://sepolia-optimistic.etherscan.io`
Block time	2 seconds	2 seconds
Withdrawal period	7 days	~12 seconds (testnet)

Alternative RPCs

Provider	Endpoint
Alchemy	`https://opt-mainnet.g.alchemy.com/v2/<KEY>`
Infura	`https://optimism-mainnet.infura.io/v3/<KEY>`
QuickNode	Custom endpoint per project
Conduit	`https://rpc.optimism.io`

Deployment

OP Mainnet is EVM-equivalent. Deploy exactly as you would to Ethereum.

Foundry

# Deploy to OP Mainnet
forge create src/MyContract.sol:MyContract \
  --rpc-url $OP_MAINNET_RPC \
  --private-key $PRIVATE_KEY \
  --broadcast

# Deploy with constructor args
forge create src/MyToken.sol:MyToken \
  --rpc-url $OP_MAINNET_RPC \
  --private-key $PRIVATE_KEY \
  --constructor-args "MyToken" "MTK" 18 \
  --broadcast

# Deploy via script
forge script script/Deploy.s.sol:DeployScript \
  --rpc-url $OP_MAINNET_RPC \
  --private-key $PRIVATE_KEY \
  --broadcast \
  --verify \
  --etherscan-api-key $ETHERSCAN_API_KEY

Hardhat

// hardhat.config.ts
import { HardhatUserConfig } from "hardhat/config";
import "@nomicfoundation/hardhat-toolbox";

const config: HardhatUserConfig = {
  solidity: "0.8.24",
  networks: {
    optimism: {
      url: process.env.OP_MAINNET_RPC || "https://mainnet.optimism.io",
      accounts: [process.env.PRIVATE_KEY!],
    },
    optimismSepolia: {
      url: process.env.OP_SEPOLIA_RPC || "https://sepolia.optimism.io",
      accounts: [process.env.PRIVATE_KEY!],
    },
  },
  etherscan: {
    apiKey: {
      optimisticEthereum: process.env.ETHERSCAN_API_KEY!,
      optimisticSepolia: process.env.ETHERSCAN_API_KEY!,
    },
  },
};

export default config;

npx hardhat run scripts/deploy.ts --network optimism

Verification

Foundry

# Verify after deployment
forge verify-contract <DEPLOYED_ADDRESS> src/MyContract.sol:MyContract \
  --chain-id 10 \
  --etherscan-api-key $ETHERSCAN_API_KEY

# Verify with constructor args
forge verify-contract <DEPLOYED_ADDRESS> src/MyToken.sol:MyToken \
  --chain-id 10 \
  --etherscan-api-key $ETHERSCAN_API_KEY \
  --constructor-args $(cast abi-encode "constructor(string,string,uint8)" "MyToken" "MTK" 18)

Hardhat

npx hardhat verify --network optimism <DEPLOYED_ADDRESS> "MyToken" "MTK" 18

Blockscout

OP Mainnet also has a Blockscout explorer at https://optimism.blockscout.com. Verification works via the standard Blockscout API — set the verifier URL in Foundry:

forge verify-contract <DEPLOYED_ADDRESS> src/MyContract.sol:MyContract \
  --verifier blockscout \
  --verifier-url https://optimism.blockscout.com/api/

Cross-Chain Messaging

The CrossDomainMessenger is the canonical way to send arbitrary messages between L1 and L2. It handles replay protection, sender authentication, and gas forwarding.

Architecture

L1 → L2 (Deposits):
  User → L1CrossDomainMessenger → OptimismPortal → L2CrossDomainMessenger → Target

L2 → L1 (Withdrawals):
  User → L2CrossDomainMessenger → L2ToL1MessagePasser → [7 day wait] → OptimismPortal → L1CrossDomainMessenger → Target

L1 → L2 Message (Deposit)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

interface IL1CrossDomainMessenger {
    function sendMessage(
        address _target,
        bytes calldata _message,
        uint32 _minGasLimit
    ) external payable;
}

contract L1Sender {
    IL1CrossDomainMessenger public immutable messenger;

    constructor(address _messenger) {
        messenger = IL1CrossDomainMessenger(_messenger);
    }

    /// @notice Send a message from L1 to a contract on L2.
    /// @param l2Target The L2 contract address to call.
    /// @param message The calldata to send to the L2 target.
    /// @param minGasLimit Minimum gas for L2 execution. Overestimate — unused gas is NOT refunded to L1.
    function sendToL2(
        address l2Target,
        bytes calldata message,
        uint32 minGasLimit
    ) external payable {
        messenger.sendMessage{value: msg.value}(l2Target, message, minGasLimit);
    }
}

L2 → L1 Message (Withdrawal)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

interface IL2CrossDomainMessenger {
    function sendMessage(
        address _target,
        bytes calldata _message,
        uint32 _minGasLimit
    ) external payable;

    function xDomainMessageSender() external view returns (address);
}

contract L2Sender {
    /// @dev L2CrossDomainMessenger predeploy address — same on all OP Stack chains
    IL2CrossDomainMessenger public constant MESSENGER =
        IL2CrossDomainMessenger(0x4200000000000000000000000000000000000007);

    function sendToL1(
        address l1Target,
        bytes calldata message,
        uint32 minGasLimit
    ) external payable {
        MESSENGER.sendMessage{value: msg.value}(l1Target, message, minGasLimit);
    }
}

Receiving Cross-Chain Messages

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

interface ICrossDomainMessenger {
    function xDomainMessageSender() external view returns (address);
}

contract L2Receiver {
    ICrossDomainMessenger public constant MESSENGER =
        ICrossDomainMessenger(0x4200000000000000000000000000000000000007);

    address public immutable l1Sender;

    constructor(address _l1Sender) {
        l1Sender = _l1Sender;
    }

    modifier onlyFromL1Sender() {
        require(
            msg.sender == address(MESSENGER) &&
            MESSENGER.xDomainMessageSender() == l1Sender,
            "Not authorized L1 sender"
        );
        _;
    }

    function handleMessage(uint256 value) external onlyFromL1Sender {
        // Process the cross-chain message
    }
}

Sender Aliasing

When an L1 contract sends a message to L2, the apparent msg.sender on L2 is the aliased address:

l2Sender = l1ContractAddress + 0x1111000000000000000000000000000000001111

The CrossDomainMessenger handles un-aliasing internally. If you bypass the messenger and send directly via OptimismPortal, you must account for aliasing yourself.

Predeploy Contracts

These contracts exist at genesis on every OP Stack chain. Do not deploy them — they are already there.

Contract	Address	Purpose
L2ToL1MessagePasser	`0x4200000000000000000000000000000000000016`	Initiates L2→L1 withdrawals
L2CrossDomainMessenger	`0x4200000000000000000000000000000000000007`	Sends/receives cross-chain messages
L2StandardBridge	`0x4200000000000000000000000000000000000010`	Bridges ETH and ERC20 tokens
L2ERC721Bridge	`0x4200000000000000000000000000000000000014`	Bridges ERC721 tokens
GasPriceOracle	`0x420000000000000000000000000000000000000F`	L1 data fee calculation
L1Block	`0x4200000000000000000000000000000000000015`	Exposes L1 block info on L2
WETH9	`0x4200000000000000000000000000000000000006`	Wrapped ETH
L1BlockNumber	`0x4200000000000000000000000000000000000013`	L1 block number (deprecated, use L1Block)
SequencerFeeVault	`0x4200000000000000000000000000000000000011`	Collects sequencer fees
BaseFeeVault	`0x4200000000000000000000000000000000000019`	Collects base fees
L1FeeVault	`0x420000000000000000000000000000000000001A`	Collects L1 data fees
GovernanceToken	`0x4200000000000000000000000000000000000042`	OP token on L2

Reading L1 Block Info

interface IL1Block {
    function number() external view returns (uint64);
    function timestamp() external view returns (uint64);
    function basefee() external view returns (uint256);
    function hash() external view returns (bytes32);
    function batcherHash() external view returns (bytes32);
    function l1FeeOverhead() external view returns (uint256);
    function l1FeeScalar() external view returns (uint256);
    function blobBaseFee() external view returns (uint256);
    function baseFeeScalar() external view returns (uint32);
    function blobBaseFeeScalar() external view returns (uint32);
}

// Usage
IL1Block constant L1_BLOCK = IL1Block(0x4200000000000000000000000000000000000015);
uint64 l1BlockNumber = L1_BLOCK.number();
uint256 l1BaseFee = L1_BLOCK.basefee();

Gas Model

Every OP Mainnet transaction pays two fees:

L2 execution fee — Standard EVM gas, priced by L2 basefee + optional priority fee. Calculated identically to Ethereum.
L1 data fee — Cost of posting the transaction's data to Ethereum L1 as calldata or blob data. This is the OP-specific component.

Post-Ecotone Formula (Current)

After the Ecotone upgrade (March 2024), L1 data fee uses a two-component formula based on calldata gas and blob gas:

l1DataFee = (l1BaseFeeScalar * l1BaseFee * 16 + l1BlobBaseFeeScalar * l1BlobBaseFee) * compressedTxSize / 1e6

l1BaseFee — Ethereum L1 base fee (from L1Block predeploy)
l1BlobBaseFee — EIP-4844 blob base fee (from L1Block predeploy)
l1BaseFeeScalar — System-configured scalar for calldata cost component
l1BlobBaseFeeScalar — System-configured scalar for blob cost component
compressedTxSize — Estimated compressed size of the signed transaction

GasPriceOracle

interface IGasPriceOracle {
    /// @notice Estimate L1 data fee for raw signed transaction bytes
    function getL1Fee(bytes memory _data) external view returns (uint256);

    /// @notice Get current L1 base fee (read from L1Block)
    function l1BaseFee() external view returns (uint256);

    /// @notice Ecotone: get blob base fee
    function blobBaseFee() external view returns (uint256);

    /// @notice Ecotone: get base fee scalar
    function baseFeeScalar() external view returns (uint32);

    /// @notice Ecotone: get blob base fee scalar
    function blobBaseFeeScalar() external view returns (uint32);

    /// @notice Check if Ecotone is active
    function isEcotone() external view returns (bool);

    /// @notice Check if Fjord is active
    function isFjord() external view returns (bool);

    /// @notice Fjord: estimate compressed size using FastLZ
    function getL1GasUsed(bytes memory _data) external view returns (uint256);
}

IGasPriceOracle constant GAS_ORACLE =
    IGasPriceOracle(0x420000000000000000000000000000000000000F);

Estimating Total Cost in TypeScript

import { createPublicClient, http, parseAbi } from "viem";
import { optimism } from "viem/chains";

const client = createPublicClient({
  chain: optimism,
  transport: http(),
});

const GAS_ORACLE = "0x420000000000000000000000000000000000000F" as const;

const gasPriceOracleAbi = parseAbi([
  "function getL1Fee(bytes memory _data) external view returns (uint256)",
  "function l1BaseFee() external view returns (uint256)",
  "function blobBaseFee() external view returns (uint256)",
  "function baseFeeScalar() external view returns (uint32)",
  "function blobBaseFeeScalar() external view returns (uint32)",
]);

async function estimateTotalCost(serializedTx: `0x${string}`) {
  const [l2GasEstimate, gasPrice, l1DataFee] = await Promise.all([
    client.estimateGas({ data: serializedTx }),
    client.getGasPrice(),
    client.readContract({
      address: GAS_ORACLE,
      abi: gasPriceOracleAbi,
      functionName: "getL1Fee",
      args: [serializedTx],
    }),
  ]);

  const l2ExecutionFee = l2GasEstimate * gasPrice;
  const totalFee = l2ExecutionFee + l1DataFee;

  return {
    l2ExecutionFee,
    l1DataFee,
    totalFee,
  };
}

Gas Optimization Tips

Minimize calldata: the L1 data fee scales with transaction data size. Fewer bytes = lower L1 fee.
Use 0 bytes when possible: zero bytes cost 4 gas in calldata vs 16 gas for non-zero bytes.
Batch operations: one large transaction costs less in L1 data fee overhead than many small ones.
After Ecotone, blob pricing makes L1 data fees much cheaper and more stable than pre-Ecotone calldata pricing.

Standard Bridge

The Standard Bridge enables ETH and ERC20 transfers between L1 and L2. It is a pair of contracts: L1StandardBridge on Ethereum and L2StandardBridge (predeploy) on OP Mainnet.

Bridge ETH: L1 → L2

interface IL1StandardBridge {
    /// @notice Bridge ETH to L2. Appears at recipient address on L2 after ~1-3 min.
    function depositETH(uint32 _minGasLimit, bytes calldata _extraData) external payable;

    /// @notice Bridge ETH to a different address on L2.
    function depositETHTo(
        address _to,
        uint32 _minGasLimit,
        bytes calldata _extraData
    ) external payable;
}

Bridge ETH: L2 → L1

interface IL2StandardBridge {
    /// @notice Initiate ETH withdrawal to L1. Requires prove + finalize after 7 days.
    function withdraw(
        address _l2Token,
        uint256 _amount,
        uint32 _minGasLimit,
        bytes calldata _extraData
    ) external payable;
}

// Withdraw ETH from L2 to L1
// _l2Token = 0xDeadDeAddeAddEAddeadDEaDDEAdDeaDDeAD0000 (legacy ETH representation)
// Send ETH as msg.value, set _amount to the same value

Bridge ERC20: L1 → L2

interface IL1StandardBridge {
    /// @notice Bridge ERC20 to L2. Token must have a corresponding L2 representation.
    function depositERC20(
        address _l1Token,
        address _l2Token,
        uint256 _amount,
        uint32 _minGasLimit,
        bytes calldata _extraData
    ) external;

    function depositERC20To(
        address _l1Token,
        address _l2Token,
        uint256 _amount,
        address _to,
        uint32 _minGasLimit,
        bytes calldata _extraData
    ) external;
}

Bridge ERC20: L2 → L1

interface IL2StandardBridge {
    function withdraw(
        address _l2Token,
        uint256 _amount,
        uint32 _minGasLimit,
        bytes calldata _extraData
    ) external payable;

    function withdrawTo(
        address _l2Token,
        address _to,
        uint256 _amount,
        uint32 _minGasLimit,
        bytes calldata _extraData
    ) external payable;
}

Withdrawal Lifecycle (L2 → L1)

Every L2→L1 withdrawal requires three L1 transactions:

Initiate — Call withdraw on L2StandardBridge or L2CrossDomainMessenger. Produces a withdrawal hash.
Prove — After the L2 output root containing your withdrawal is proposed on L1 (~1 hour), call proveWithdrawalTransaction on OptimismPortal.
Finalize — After the 7-day challenge period, call finalizeWithdrawalTransaction on OptimismPortal.

import { getWithdrawals, getL2Output } from "viem/op-stack";

// After initiating withdrawal on L2, get the receipt
const l2Receipt = await publicClient.getTransactionReceipt({ hash: l2TxHash });

// Build withdrawal proof (after output root is proposed, ~1 hour)
const output = await getL2Output(l1Client, {
  l2BlockNumber: l2Receipt.blockNumber,
  targetChain: optimism,
});

// Prove on L1
const proveHash = await walletClient.proveWithdrawal({
  output,
  withdrawal: withdrawals[0],
  targetChain: optimism,
});

// Wait 7 days, then finalize on L1
const finalizeHash = await walletClient.finalizeWithdrawal({
  withdrawal: withdrawals[0],
  targetChain: optimism,
});

SuperchainERC20

SuperchainERC20 is a cross-chain token standard enabling native token transfers between OP Stack chains in the Superchain. Tokens implementing this standard can move between chains without traditional bridge locking.

Interface

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";

/// @notice Interface for tokens that support cross-chain transfers within the Superchain.
interface ICrosschainERC20 {
    /// @notice Emitted when tokens are minted via a cross-chain transfer.
    event CrosschainMint(address indexed to, uint256 amount, address indexed sender);

    /// @notice Emitted when tokens are burned for a cross-chain transfer.
    event CrosschainBurn(address indexed from, uint256 amount, address indexed sender);

    /// @notice Mint tokens on this chain as part of a cross-chain transfer.
    /// @dev Only callable by the SuperchainTokenBridge.
    function crosschainMint(address _to, uint256 _amount) external;

    /// @notice Burn tokens on this chain to initiate a cross-chain transfer.
    /// @dev Only callable by the SuperchainTokenBridge.
    function crosschainBurn(address _from, uint256 _amount) external;
}

Implementation

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import {ERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import {ICrosschainERC20} from "./ICrosschainERC20.sol";

/// @dev SuperchainTokenBridge predeploy address — same on all OP Stack chains
address constant SUPERCHAIN_TOKEN_BRIDGE = 0x4200000000000000000000000000000000000028;

contract MySuperchainToken is ERC20, ICrosschainERC20 {
    constructor() ERC20("MySuperchainToken", "MST") {
        _mint(msg.sender, 1_000_000 * 1e18);
    }

    function crosschainMint(address _to, uint256 _amount) external override {
        require(msg.sender == SUPERCHAIN_TOKEN_BRIDGE, "Only bridge");
        _mint(_to, _amount);
        emit CrosschainMint(_to, _amount, msg.sender);
    }

    function crosschainBurn(address _from, uint256 _amount) external override {
        require(msg.sender == SUPERCHAIN_TOKEN_BRIDGE, "Only bridge");
        _burn(_from, _amount);
        emit CrosschainBurn(_from, _amount, msg.sender);
    }
}

Cross-Chain Transfer Flow

User calls SuperchainTokenBridge.sendERC20 on the source chain
Bridge calls crosschainBurn on the token contract (burns on source)
A cross-chain message is relayed to the destination chain
Bridge calls crosschainMint on the destination chain's token contract (mints on destination)

OP Stack

The OP Stack is the modular, open-source framework for building L2 blockchains. OP Mainnet, Base, Zora, Mode, and others are all OP Stack chains forming the Superchain.

Key Components

Component	Description
op-node	Consensus client — derives L2 blocks from L1 data
op-geth	Execution client — modified go-ethereum
op-batcher	Posts transaction data to L1 (calldata or blobs)
op-proposer	Proposes L2 output roots to L1
op-challenger	Runs fault proof games to challenge invalid proposals

Superchain

The Superchain is a network of OP Stack chains sharing:

Bridge contracts on L1
Sequencer coordination
Governance via the Optimism Collective
Interoperability messaging

Current Superchain members include OP Mainnet, Base, Zora, Mode, Fraxtal, Metal, and others. All share the same upgrade path and security model.

Building a Custom OP Chain

Use the OP Stack to launch your own chain:

# Clone the optimism monorepo
git clone https://github.com/ethereum-optimism/optimism.git
cd optimism

# Install dependencies
pnpm install

# Configure your chain (edit deploy-config)
# Deploy L1 contracts
# Start op-node, op-geth, op-batcher, op-proposer

Refer to the OP Stack Getting Started Guide for complete chain deployment.

Governance

The Optimism Collective governs the protocol through a bicameral system:

Token House — OP token holders vote on protocol upgrades, incentive programs, and treasury allocations
Citizens' House — Soulbound "citizen" badges vote on retroactive public goods funding (RetroPGF)

OP Token

Property	Value
Address (L2)	`0x4200000000000000000000000000000000000042`
Address (L1)	`0x4200000000000000000000000000000000000042` is the L2 predeploy; L1 address is `0x4200000000000000000000000000000000000042` bridged
Total supply	4,294,967,296 (2^32)
Type	Governance only (no fee burn or staking yield)

Delegation

OP token holders delegate voting power to active governance participants:

import { parseAbi } from "viem";

const opTokenAbi = parseAbi([
  "function delegate(address delegatee) external",
  "function delegates(address account) external view returns (address)",
  "function getVotes(address account) external view returns (uint256)",
]);

const OP_TOKEN = "0x4200000000000000000000000000000000000042" as const;

// Delegate voting power
const hash = await walletClient.writeContract({
  address: OP_TOKEN,
  abi: opTokenAbi,
  functionName: "delegate",
  args: [delegateAddress],
});

Key Differences from Ethereum

Feature	Ethereum	OP Mainnet
Block time	12 seconds	2 seconds
Gas pricing	Single base fee	L2 execution + L1 data fee
`block.number`	L1 block number	L2 block number
Finality	~15 minutes (2 epochs)	7 days for L2→L1 (challenge period)
Sequencing	Decentralized validators	Centralized sequencer (OP Labs)
`PREVRANDAO`	Beacon chain randomness	Sequencer-set value (NOT random, do NOT use for randomness)
`PUSH0`	Supported (Shanghai+)	Supported
`block.difficulty`	Always 0 post-merge	Always 0

Opcodes Differences

PREVRANDAO (formerly DIFFICULTY) — Returns the sequencer-set value, NOT true randomness. Never use for on-chain randomness. Use Chainlink VRF or a commit-reveal scheme.
ORIGIN / CALLER — Work normally for L2 transactions. For L1→L2 deposits, the origin is aliased (see Sender Aliasing).
All other opcodes behave identically to Ethereum.

Unsupported Features

No native account abstraction (EIP-4337) — Use third-party bundlers (Pimlico, Alchemy, Stackup).
No eth_getProof with pending block tag — Use latest instead.