Foundry Development for EVM Chains

This skill covers Foundry setup and development for EVM-compatible chains with emphasis on Celo.

When to Use

• Setting up a new Foundry project
• Writing and compiling Solidity smart contracts with forge
• Testing contracts with forge test
• Deploying contracts to Celo or other EVM chains
• Verifying contracts on block explorers
• Interacting with contracts using cast

Foundry Tools

Tool	Purpose
forge	Build, test, debug, deploy, and verify smart contracts
cast	Interact with contracts and retrieve chain data from CLI
anvil	Run a local Ethereum development node with forking support
chisel	Fast Solidity REPL for interactive development

Installation

# Install Foundryup (the Foundry installer)
curl -L https://foundry.paradigm.xyz | bash

# Install Foundry tools
foundryup

For Windows, use Git BASH or WSL (Foundryup doesn't support PowerShell or Command Prompt).

Quick Start

Initialize Project

forge init my-project
cd my-project

Project Structure

my-project/
├── foundry.toml      # Configuration
├── src/              # Contract source files
│   └── Counter.sol
├── test/             # Test files
│   └── Counter.t.sol
├── script/           # Deployment scripts
│   └── Counter.s.sol
└── lib/              # Dependencies

Celo Network Information

Network	Chain ID	RPC Endpoint
Celo Mainnet	42220	https://forno.celo.org
Celo Sepolia	11142220	https://forno.celo-sepolia.celo-testnet.org

Configuration

foundry.toml for Celo

[profile.default]
src = "src"
out = "out"
libs = ["lib"]
solc = "0.8.28"
optimizer = true
optimizer_runs = 200

[rpc_endpoints]
celo = "https://forno.celo.org"
celo_sepolia = "https://forno.celo-sepolia.celo-testnet.org"
localhost = "http://127.0.0.1:8545"

[etherscan]
celo = { key = "${CELOSCAN_API_KEY}", chain = 42220, url = "https://api.celoscan.io/api" }
celo_sepolia = { key = "${CELOSCAN_API_KEY}", chain = 11142220, url = "https://api.etherscan.io/v2/api" }

Environment Variables (.env)

PRIVATE_KEY=your_private_key_here
CELOSCAN_API_KEY=your_celoscan_api_key_here

Load environment variables:

source .env

Writing Contracts

Basic Contract

// src/MyContract.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.28;

contract MyContract {
    string public name;
    address public owner;

    event NameChanged(string oldName, string newName);

    modifier onlyOwner() {
        require(msg.sender == owner, "Not owner");
        _;
    }

    constructor(string memory _name) {
        name = _name;
        owner = msg.sender;
    }

    function setName(string memory _newName) external onlyOwner {
        string memory oldName = name;
        name = _newName;
        emit NameChanged(oldName, _newName);
    }
}

Using OpenZeppelin

forge install OpenZeppelin/openzeppelin-contracts

Add to remappings.txt:

@openzeppelin/contracts/=lib/openzeppelin-contracts/contracts/

// src/MyToken.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.28;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract MyToken is ERC20, Ownable {
    constructor() ERC20("MyToken", "MTK") Ownable(msg.sender) {
        _mint(msg.sender, 1000000 * 10 ** decimals());
    }

    function mint(address to, uint256 amount) external onlyOwner {
        _mint(to, amount);
    }
}

Compilation

# Compile all contracts
forge build

# Clean and rebuild
forge clean && forge build

# Check contract sizes
forge build --sizes

Testing

Test File Structure

// test/MyContract.t.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.28;

import {Test, console} from "forge-std/Test.sol";
import {MyContract} from "../src/MyContract.sol";

contract MyContractTest is Test {
    MyContract public myContract;
    address public owner;
    address public user;

    function setUp() public {
        owner = address(this);
        user = makeAddr("user");
        myContract = new MyContract("Initial Name");
    }

    function test_InitialName() public view {
        assertEq(myContract.name(), "Initial Name");
    }

    function test_Owner() public view {
        assertEq(myContract.owner(), owner);
    }

    function test_SetName() public {
        myContract.setName("New Name");
        assertEq(myContract.name(), "New Name");
    }

    function test_SetNameEmitsEvent() public {
        vm.expectEmit(true, true, true, true);
        emit MyContract.NameChanged("Initial Name", "New Name");
        myContract.setName("New Name");
    }

    function test_RevertWhen_NonOwnerSetsName() public {
        vm.prank(user);
        vm.expectRevert("Not owner");
        myContract.setName("Hacked");
    }

    function testFuzz_SetName(string memory newName) public {
        myContract.setName(newName);
        assertEq(myContract.name(), newName);
    }
}

Running Tests

# Run all tests
forge test

# Run with verbosity (show logs)
forge test -vvv

# Run specific test
forge test --match-test test_SetName

# Run specific contract
forge test --match-contract MyContractTest

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

# Run with coverage
forge coverage

# Fork testing against Celo mainnet
forge test --fork-url https://forno.celo.org

Deployment

Deployment Script

// script/Deploy.s.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.28;

import {Script, console} from "forge-std/Script.sol";
import {MyContract} from "../src/MyContract.sol";

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

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

        vm.startBroadcast(deployerPrivateKey);

        MyContract myContract = new MyContract("My Contract Name");
        console.log("Contract deployed to:", address(myContract));

        vm.stopBroadcast();
    }
}

Deploy Commands

# Deploy to local Anvil
forge script script/Deploy.s.sol --rpc-url http://127.0.0.1:8545 --broadcast

# Deploy to Celo Sepolia
forge script script/Deploy.s.sol --rpc-url https://forno.celo-sepolia.celo-testnet.org --broadcast --private-key $PRIVATE_KEY

# Deploy to Celo Mainnet
forge script script/Deploy.s.sol --rpc-url https://forno.celo.org --broadcast --private-key $PRIVATE_KEY

# Deploy with verification
forge script script/Deploy.s.sol --rpc-url https://forno.celo-sepolia.celo-testnet.org --broadcast --verify --private-key $PRIVATE_KEY

Quick Deploy with forge create

# Deploy to Celo Sepolia
forge create src/MyContract.sol:MyContract \
  --rpc-url https://forno.celo-sepolia.celo-testnet.org \
  --private-key $PRIVATE_KEY \
  --constructor-args "My Contract Name"

# Deploy with verification
forge create src/MyContract.sol:MyContract \
  --rpc-url https://forno.celo-sepolia.celo-testnet.org \
  --private-key $PRIVATE_KEY \
  --constructor-args "My Contract Name" \
  --verify \
  --etherscan-api-key $CELOSCAN_API_KEY

Verification

Verify Existing Contract

# Verify on Celo Sepolia
forge verify-contract \
  --chain-id 11142220 \
  <CONTRACT_ADDRESS> \
  src/MyContract.sol:MyContract \
  --etherscan-api-key $CELOSCAN_API_KEY \
  --watch

# Verify on Celo Mainnet
forge verify-contract \
  --chain-id 42220 \
  <CONTRACT_ADDRESS> \
  src/MyContract.sol:MyContract \
  --etherscan-api-key $CELOSCAN_API_KEY \
  --watch

# With constructor arguments
forge verify-contract \
  --chain-id 11142220 \
  <CONTRACT_ADDRESS> \
  src/MyContract.sol:MyContract \
  --etherscan-api-key $CELOSCAN_API_KEY \
  --constructor-args $(cast abi-encode "constructor(string)" "My Contract Name") \
  --watch

Cast Commands

Reading Data

# Get balance
cast balance <ADDRESS> --rpc-url https://forno.celo.org

# Call view function
cast call <CONTRACT_ADDRESS> "name()(string)" --rpc-url https://forno.celo.org

# Get storage slot
cast storage <CONTRACT_ADDRESS> 0 --rpc-url https://forno.celo.org

# Get block number
cast block-number --rpc-url https://forno.celo.org

Writing Data

# Send transaction
cast send <CONTRACT_ADDRESS> "setName(string)" "New Name" \
  --rpc-url https://forno.celo.org \
  --private-key $PRIVATE_KEY

# Transfer CELO
cast send <TO_ADDRESS> --value 1ether \
  --rpc-url https://forno.celo.org \
  --private-key $PRIVATE_KEY

Utility Commands

# Encode function call
cast calldata "setName(string)" "New Name"

# Decode function call
cast 4byte-decode <CALLDATA>

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

# Get ABI-encoded constructor args
cast abi-encode "constructor(string)" "My Contract Name"

Anvil (Local Node)

# Start local node
anvil

# Start with fork of Celo mainnet
anvil --fork-url https://forno.celo.org

# Start with specific block
anvil --fork-url https://forno.celo.org --fork-block-number 12345678

Block Explorers

• Celo Mainnet: https://celoscan.io
• Celo Sepolia: https://sepolia.celoscan.io

Additional Resources

• foundry-config.md - Detailed configuration options
• testing-patterns.md - Advanced testing patterns
• security-checklist.md - Security best practices

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Source of truth: Celopedia

These skills are focused, task-level references. For anything broader — verified contract addresses, ecosystem and protocol data, listing requirements, grants, governance, migration guides, or cross-cutting Celo questions — Celopedia is the canonical source and is kept current. Where this skill and Celopedia disagree, Celopedia wins.

npx skills add celo-org/celopedia-skills