Foundry Framework Skill

Expert-level usage of Foundry, the blazing fast, portable, and modular toolkit for Ethereum application development.

Capabilities

• Forge Testing: Write and run Solidity tests with fuzzing
• Gas Optimization: Generate detailed gas reports and snapshots
• Local Development: Use Anvil for local blockchain
• Chain Interaction: Execute Cast commands for on-chain operations
• Project Configuration: Set up foundry.toml for projects
• Deployment Scripts: Write and run forge scripts
• REPL Debugging: Use Chisel for Solidity exploration

Installation

# Install Foundry
curl -L https://foundry.paradigm.xyz | bash

# Update to latest
foundryup

# Verify installation
forge --version
cast --version
anvil --version
chisel --version

Project Setup

Initialize Project

# New project
forge init my_project
cd my_project

# Add dependencies
forge install OpenZeppelin/openzeppelin-contracts
forge install foundry-rs/forge-std

foundry.toml Configuration

[profile.default]
src = "src"
out = "out"
libs = ["lib"]
solc = "0.8.20"
optimizer = true
optimizer_runs = 200
via_ir = false

[profile.default.fuzz]
runs = 256
max_test_rejects = 65536
seed = "0x1234"

[profile.default.invariant]
runs = 256
depth = 15
fail_on_revert = false

[profile.ci]
fuzz = { runs = 10000 }
invariant = { runs = 1000, depth = 50 }

[rpc_endpoints]
mainnet = "${MAINNET_RPC_URL}"
sepolia = "${SEPOLIA_RPC_URL}"
arbitrum = "${ARBITRUM_RPC_URL}"

[etherscan]
mainnet = { key = "${ETHERSCAN_API_KEY}" }
sepolia = { key = "${ETHERSCAN_API_KEY}" }

Forge Testing

Basic Test

// test/Counter.t.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "forge-std/Test.sol";
import "../src/Counter.sol";

contract CounterTest is Test {
    Counter public counter;

    function setUp() public {
        counter = new Counter();
        counter.setNumber(0);
    }

    function test_Increment() public {
        counter.increment();
        assertEq(counter.number(), 1);
    }

    function testFail_Underflow() public {
        counter.decrement();
    }
}

Fuzz Testing

contract FuzzTest is Test {
    function testFuzz_SetNumber(uint256 x) public {
        counter.setNumber(x);
        assertEq(counter.number(), x);
    }

    function testFuzz_BoundedInput(uint256 x) public {
        x = bound(x, 1, 100);
        // x is now between 1 and 100
    }
}

Invariant Testing

contract InvariantTest is Test {
    Counter public counter;

    function setUp() public {
        counter = new Counter();
        targetContract(address(counter));
    }

    function invariant_NumberNeverNegative() public {
        assertTrue(counter.number() >= 0);
    }

    function invariant_NumberUnderMax() public {
        assertTrue(counter.number() < type(uint256).max);
    }
}

Fork Testing

contract ForkTest is Test {
    function setUp() public {
        // Fork mainnet at specific block
        vm.createSelectFork("mainnet", 18000000);
    }

    function test_MainnetState() public {
        // Interact with mainnet contracts
        IERC20 dai = IERC20(0x6B175474E89094C44Da98b954EescdeCB5c811d7);
        uint256 balance = dai.balanceOf(address(this));
    }
}

Forge Commands

# Build project
forge build

# Run tests
forge test

# Run tests with verbosity
forge test -vvvv

# Run specific test
forge test --match-test testFuzz_SetNumber

# Run tests with gas report
forge test --gas-report

# Generate gas snapshot
forge snapshot

# Compare gas snapshots
forge snapshot --diff

# Coverage
forge coverage

# Format code
forge fmt

Cast Commands

Read Chain Data

# Get ETH balance
cast balance 0x... --rpc-url $RPC

# Read contract storage
cast storage 0x... 0 --rpc-url $RPC

# Call view function
cast call 0x... "balanceOf(address)" 0x... --rpc-url $RPC

# Decode calldata
cast calldata-decode "transfer(address,uint256)" 0x...

Send Transactions

# Send ETH
cast send 0x... --value 1ether --rpc-url $RPC --private-key $KEY

# Call contract function
cast send 0x... "transfer(address,uint256)" 0x... 1000 --rpc-url $RPC --private-key $KEY

Utility Commands

# Convert units
cast to-wei 1 ether
cast from-wei 1000000000000000000

# Compute function selector
cast sig "transfer(address,uint256)"

# Get ABI
cast abi-encode "transfer(address,uint256)" 0x... 100

# Decode ABI
cast abi-decode "balanceOf(address)(uint256)" 0x...

Anvil Local Node

# Start local node
anvil

# Start with specific chain ID
anvil --chain-id 31337

# Fork mainnet
anvil --fork-url $MAINNET_RPC

# Fork at specific block
anvil --fork-url $MAINNET_RPC --fork-block-number 18000000

# Preload accounts
anvil --accounts 20 --balance 10000

Anvil RPC

# Impersonate account
cast rpc anvil_impersonateAccount 0x... --rpc-url http://localhost:8545

# Set balance
cast rpc anvil_setBalance 0x... 0x1000000000000000000 --rpc-url http://localhost:8545

# Mine blocks
cast rpc anvil_mine 10 --rpc-url http://localhost:8545

# Set block timestamp
cast rpc evm_setNextBlockTimestamp 1700000000 --rpc-url http://localhost:8545

Deployment Scripts

Script Example

// script/Deploy.s.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "forge-std/Script.sol";
import "../src/Counter.sol";

contract DeployScript is Script {
    function setUp() public {}

    function run() public {
        uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");

        vm.startBroadcast(deployerPrivateKey);

        Counter counter = new Counter();
        counter.setNumber(42);

        vm.stopBroadcast();

        console.log("Counter deployed at:", address(counter));
    }
}

Run Scripts

# Simulate deployment
forge script script/Deploy.s.sol --rpc-url $RPC

# Deploy to network
forge script script/Deploy.s.sol --rpc-url $RPC --broadcast

# Verify on Etherscan
forge script script/Deploy.s.sol --rpc-url $RPC --broadcast --verify

Chisel REPL

# Start Chisel
chisel

# In REPL
> uint256 x = 100
> x * 2
200
> address(this)
0x...

Process Integration

Process	Purpose
smart-contract-development-lifecycle.js	Full development
smart-contract-fuzzing.js	Fuzzing and invariant testing
invariant-testing.js	Property-based testing
gas-optimization.js	Gas profiling
All DeFi processes	Testing and deployment

Best Practices

1. Use forge fmt before committing
2. Maintain gas snapshots for regression testing
3. Use fork testing for integration tests
4. Set appropriate fuzz runs for CI
5. Use profile-based configuration
6. Keep foundry.toml in version control

See Also

• skills/hardhat-framework/SKILL.md - Alternative framework
• skills/echidna-fuzzer/SKILL.md - Advanced fuzzing
• skills/gas-optimization/SKILL.md - Gas optimization
• Foundry Book