# Invoke this skill for Ethereum development
Skill("ethereum-development", topic="gas", network="mainnet")

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

contract Optimized {
    // Pack into single slot (32 bytes)
    struct User {
        uint128 balance;    // 16 bytes
        uint64 lastUpdate;  // 8 bytes
        uint32 nonce;       // 4 bytes
        bool active;        // 1 byte
        // 3 bytes padding
    }

    mapping(address => User) public users;
}

import { createPublicClient, http, keccak256, encodePacked, pad } from 'viem';
import { mainnet } from 'viem/chains';

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

// Read mapping value: balances[address]
async function getBalance(contract: `0x${string}`, user: `0x${string}`) {
  const slot = keccak256(encodePacked(['address', 'uint256'], [user, 0n]));
  return await client.getStorageAt({ address: contract, slot });
}

import { createWalletClient, http, parseEther } from 'viem';

const client = createWalletClient({ transport: http() });

const hash = await client.sendTransaction({
  to: '0x...',
  value: parseEther('0.1'),
  type: 'eip1559',
  maxFeePerGas: parseGwei('30'),
  maxPriorityFeePerGas: parseGwei('2'),
});

# Check current gas prices
cast gas-price --rpc-url $RPC
cast basefee --rpc-url $RPC

# Trace transaction to find issue
cast run --trace $TX_HASH --rpc-url $RPC

# Get current nonce
cast nonce $ADDRESS --rpc-url $RPC

# Foundry essentials
forge build --sizes          # Contract sizes
forge test --gas-report      # Gas consumption
forge snapshot               # Gas snapshots
cast storage $ADDR $SLOT     # Read storage
cast call $ADDR "fn()"       # Simulate call

contract GasTest is Test {
    function test_GasOptimization() public {
        uint256 gasBefore = gasleft();
        target.optimizedFunction();
        uint256 gasUsed = gasBefore - gasleft();

        assertLt(gasUsed, 50000, "Too much gas used");
    }
}