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A smart contract is a program uploaded to the blockchain. No bank in the middle, no company. It runs automatically between two parties and nobody can interfere. Most of what you see in DeFi and NFTs is built on top of this.

Arc is an EVM-compatible blockchain that can run these contracts. Its most fundamental difference from Ethereum is that gas fees are paid in USDC instead of ETH. Arc is a stablecoin-focused L1 currently in testnet, with an ecosystem that genuinely supports developers.

In this guide we'll deploy a smart contract to Arc Testnet from scratch using Foundry, covering every detail.

A development tool for writing, testing, and deploying smart contracts. It doesn't run in a browser, it runs in your computer's terminal. The terminal is the black screen where you type commands and press Enter. On Mac it comes pre-installed. On Windows it requires additional setup.

Open the Terminal app on your Mac. Paste the following three commands one by one, press Enter after each one, and wait for it to finish:

Once installation is complete, don't close the Terminal and continue from here.

To run Foundry on Windows you first need to install WSL. WSL lets you open a Linux terminal inside Windows.

Type PowerShell in the search bar, right-click it, and select "Run as administrator." Paste the following and press Enter:

Restart your computer after installation. Open Ubuntu from the Start menu. On first launch it will ask you to create a username and password. Set these and write them down somewhere, it will ask for this password in future sessions.

Foundry Installation (inside the Ubuntu terminal):

Open VS Code. Click the icon made of four squares on the left sidebar. Type WSL in the search box. Find the WSL extension developed by Microsoft and click Install. Close and reopen VS Code after installation. You can now type 

 in the Ubuntu terminal to open that folder in VS Code.

From this point on, if you're on Mac continue in Terminal, if you're on Windows continue in the Ubuntu terminal. The commands are the same on both systems.

Running this command creates a project folder called arc-greeter and the terminal automatically enters that folder. The 

 sign runs two separate commands back to back so you don't have to type them one at a time.

RPC is the address your program uses to connect to Arc Testnet. We save it to a file so we don't have to type it every time.

This command created an empty file called .env inside your project folder. Open it:

The screen will change and an editor with GNU nano at the top will open. Mouse doesn't work in this editor, everything is done with the keyboard. Copy and paste the following line into the terminal. On Mac use Cmd+V, on Windows use Ctrl+Shift+V.

ARC_TESTNET_RPC_URL="https://rpc.testnet.arc.network"

To save: press Ctrl+X together, then press Y, then press Enter. When you're back in the terminal the file is saved.

The terminal will give you output that looks like this:

The address is your public identity, you can share it with anyone. The private key is your wallet's password. Anyone who knows it has full access to your account. Copy both to a safe place, you'll need them in the steps ahead.

Now let's add the private key to the .env file:

You'll see the line you wrote earlier. Use the arrow keys to go to the bottom, press Enter to open a new line, and paste:

 with the private key you copied. To save: press Ctrl+X together, the screen will ask something, press Y, then press Enter. Then run:

This command introduced the contents of the .env file to the terminal. Now whenever you type 

 the terminal will automatically use the real value. Whenever you add something new to the file you need to run this command again.

Every transaction on Arc requires USDC. Testnet USDC has no real value, it's only for testing.

Go to faucet.circle.com in your browser. Select Arc Testnet as the network. Enter the value from the Address line you saw in Step 3, not the private key. Submit it and testnet USDC will arrive in your wallet within a few seconds.

Foundry puts an example file in the project when it's created. Remove it with this command:

An empty editor will open. Copy and paste the following code:

    event MessageUpdated(string newMessage);

    function setMessage(string memory newMessage) public {

    function getMessage() public view returns (string memory) {

This contract stores a message. You can read it and update it. Every update gets recorded on the blockchain.

Before deploying the contract we test it to make sure it works correctly. Let's remove the example files:

 is a command that deletes a folder and everything inside it. Now let's create our test file:

Copy and paste the following into the editor:

    function testInitialMessage() public view {

        string memory expected = "Hello Arc Testnet!";

        string memory actual = arcGreeter.getMessage();

        string memory newMessage = "Merhaba Arc!";

        arcGreeter.setMessage(newMessage);

    function testMessageUpdatedEvent() public {

        string memory newMessage = "Building on Arc!";

        vm.expectEmit(true, true, true, true);

        emit ArcGreeter.MessageUpdated(newMessage);

If every line starts with PASS, continue. Now build:

Copy and paste the following command as is. You don't need to type the parts starting with 

 yourself, the terminal pulls them automatically from the .env file:

forge create src/ArcGreeter.sol:ArcGreeter \

 with the address you copied. Save: Ctrl+X, Y, Enter. We added something new so let's introduce it again:

Deploying a Smart Contract to Arc Testnet-Guide for Beginners

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