Foundry

Foundry is a blazing-fast, portable, and modular toolkit for Ethereum application development. This guide shows you how to deploy smart contracts to LitVM using Foundry.

Prerequisites

• Foundry installed

• A wallet with testnet zkLTC (see Add to Your Wallet)

• Basic familiarity with Solidity

---

Install Foundry

If you haven't installed Foundry yet:

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

# Install Foundry
foundryup

Verify installation:

forge --version

---

Create a New Project

# Create new project
forge init my-litvm-project

# Navigate to project
cd my-litvm-project

This creates a project structure:

my-litvm-project/
├── lib/ # Dependencies
├── script/ # Deployment scripts
├── src/ # Contracts
├── test/ # Tests
└── foundry.toml  # Configuration

---

Write Your Contract

Create a simple contract in src/Counter.sol:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

contract Counter {
    uint256 public count;
    event CountChanged(uint256 newCount);

    function increment() public {
        count += 1;
        emit CountChanged(count);
    }

    function decrement() public {
        require(count > 0, "Count cannot go below zero");
        count -= 1;
        emit CountChanged(count);
    }

    function setCount(uint256 _count) public {
        count = _count;
        emit CountChanged(count);
    }
}

---

Configure for LitVM

Update foundry.toml to include LitVM network:

[profile.default]
src = "src"
out = "out"
libs = ["lib"]
solc = "0.8.19"

[rpc_endpoints]
litvm_testnet = "RPC_URL"
litvm_mainnet = "RPC_URL"

[explorer]
litvm_testnet = { key = "${LITVM_EXPLORER_API_KEY}", url = "EXPLORER_URL/api"}

---

Set Up Environment

Create a .env file (add to .gitignore!):

# .env
PRIVATE_KEY=your_private_key_here
LITVM_RPC_URL=RPC_URL

Load environment variables:

source .env

---

Compile

forge build

Expected output:

[⠊] Compiling...
[⠒] Compiling 1 files with 0.8.19
[⠑] Solc 0.8.19 finished in 1.23s
Compiler run successful!

---

Test

Run tests before deploying:

forge test

Add a test in test/Counter.t.sol:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;
import {Test, console} from "forge-std/Test.sol";
import {Counter} from "../src/Counter.sol";

contract CounterTest is Test {
    Counter public counter;

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

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

    function test_Decrement() public {
        counter.increment();
        counter.decrement();
        assertEq(counter.count(), 0);
    }

    function test_SetCount() public {
        counter.setCount(100);
        assertEq(counter.count(), 100);
    }

    function testFail_DecrementBelowZero() public {
        counter.decrement(); // Should fail
    }
}

Run with verbosity:

forge test -vvv

---

Deploy

1

Direct deploy

Use forge create with your RPC and private key:

forge create --rpc-url $LITVM_RPC_URL \
  --private-key $PRIVATE_KEY \
  src/Counter.sol:Counter

2

Deploy script (Recommended)

Create script/Deploy.s.sol:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;
import {Script, console} from "forge-std/Script.sol";
import {Counter} from "../src/Counter.sol";

contract DeployCounter is Script {
    function run() public {
        uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");
        vm.startBroadcast(deployerPrivateKey);
        Counter counter = new Counter();
        console.log("Counter deployed to:", address(counter));
        vm.stopBroadcast();
    }
}

Run the script:

forge script script/Deploy.s.sol:DeployCounter \
  --rpc-url $LITVM_RPC_URL \
  --broadcast

---

Verify Contract

Verify on LitVM Explorer:

forge verify-contract \
  --chain-id [LITVM_CHAIN_ID] \
  --compiler-version v0.8.19 \
  --watch \
  [DEPLOYED_CONTRACT_ADDRESS] \
  src/Counter.sol:Counter \
  --explorer-api-key $LITVM_EXPLORER_API_KEY \
  --verifier-url EXPLORER_URL

---

Interact with Contract

Using cast

# Read count
cast call [CONTRACT_ADDRESS] "count()" --rpc-url $LITVM_RPC_URL

# Increment
cast send [CONTRACT_ADDRESS] "increment()" \
  --rpc-url $LITVM_RPC_URL \
  --private-key $PRIVATE_KEY

# Set count to 42
cast send [CONTRACT_ADDRESS] "setCount(uint256)" 42 \
  --rpc-url $LITVM_RPC_URL \
  --private-key $PRIVATE_KEY

Using Forge Script

Create script/Interact.s.sol:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;
import {Script, console} from "forge-std/Script.sol";
import {Counter} from "../src/Counter.sol";

contract InteractCounter is Script {
    function run() public {
        uint256 deployerPrivateKey = vm.envUint("PRIVATE_KEY");
        address counterAddress = vm.envAddress("COUNTER_ADDRESS");
        Counter counter = Counter(counterAddress);
        vm.startBroadcast(deployerPrivateKey);
        // Increment 3 times
        counter.increment();
        counter.increment();
        counter.increment();
        console.log("New count:", counter.count());
        vm.stopBroadcast();
    }
}

---

Gas Estimation

Check gas costs before deploying:

# Estimate deployment gas
forge create --rpc-url $LITVM_RPC_URL \
  src/Counter.sol:Counter \
  --estimate

---

Common Issues

"Insufficient funds"

Ensure your wallet has testnet zkLTC. Visit the faucet.

"Nonce too low"

Reset nonce or wait for pending transactions to confirm:

cast nonce [YOUR_ADDRESS] --rpc-url $LITVM_RPC_URL

"RPC error"

• Check RPC URL is correct

• Verify network connectivity

• Try alternative RPC endpoints

---

Next Steps

• Deploy more complex contracts (ERC-20, ERC-721, etc.)

• Set up Hardhat for alternative tooling

• Explore LitVM ecosystem dApps

---

Resources

• Foundry Book

• Foundry GitHub

• LitVM Block Explorer (coming soon)