To use Foundry to build smart contracts on Abstract, use the foundry-zksync fork.

YouTube Tutorial: Get Started with Foundry

Watch a step-by-step tutorial on how to get started with Foundry.

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1. Install the foundry-zksync fork

This installation overrides any existing forge and cast binaries in ~/.foundry. To revert to the standard foundry installation, follow the Foundry installation guide. You can swap between the two installations at any time.
1

Install foundry-zksync

Install the foundryup-zksync fork:
curl -L https://raw.githubusercontent.com/matter-labs/foundry-zksync/main/install-foundry-zksync | bash
Run foundryup-zksync to install forge, cast, and anvil:
foundryup-zksync
You may need to restart your terminal session after installation to continue.
2

Verify installation

A helpful command to check if the installation was successful is:
forge build --help | grep -A 20 "ZKSync configuration:"
If installed successfully, 20 lines of --zksync options will be displayed.

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2. Create a new project

Create a new project with forge and change directory into the project. 
forge init my-abstract-project && cd my-abstract-project

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3. Modify Foundry configuration

Update your foundry.toml file to include the following options: 
[profile.default]
src = 'src'
libs = ['lib']
fallback_oz = true

[profile.default.zksync]
enable_eravm_extensions = true # Note: System contract calls (NonceHolder and ContractDeployer) can only be called with this set to true

[etherscan]
abstractTestnet = { chain = "11124", url = "https://api-sepolia.abscan.org/api", key = "TACK2D1RGYX9U7MC31SZWWQ7FCWRYQ96AD"}
abstractMainnet = { chain = "2741", url = "", key = ""} # You can replace these values or leave them blank to override via CLI
To use system contracts, set the enable_eravm_extensions flag in [profile.default.zksync] to true.

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4. Write a smart contract

Modify the src/Counter.sol file to include the following smart contract: 
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

contract Counter {
    uint256 public number;

    function setNumber(uint256 newNumber) public {
        number = newNumber;
    }

    function increment() public {
        number++;
    }
}

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5. Compile the smart contract

Use the zksolc compiler (installed in the above steps) to compile smart contracts for Abstract: 
forge build --zksync
You should now see the compiled smart contracts in the generated zkout directory.

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6. Deploy the smart contract

Add your private key

Create a new wallet keystore.
cast wallet import myKeystore --interactive
Enter your wallet’s private key when prompted and provide a password to encrypt it.
We recommend not to use a private key associated with real funds. Create a new wallet for this step.
2

Get ETH in the deployer account

The deployer account requires ETH to deploy a smart contract.
  • Testnet: Claim ETH via a faucet, or bridge ETH from Sepolia.
  • Mainnet: Use a bridge to transfer ETH to Abstract mainnet.
3

Get an Abscan API key (Mainnet only)

Follow the Abscan documentation to get an API key to verify your smart contracts on the block explorer. This is recommended; but not required.

Deploy your smart contract

Run the following command to deploy your smart contracts:
forge create src/Counter.sol:Counter \
    --account myKeystore \
    --rpc-url https://api.testnet.abs.xyz \
    --chain 11124 \
    --zksync \
    --verify \
    --verifier etherscan \
    --verifier-url https://api-sepolia.abscan.org/api \
    --etherscan-api-key TACK2D1RGYX9U7MC31SZWWQ7FCWRYQ96AD \
    --broadcast
Note: Replace the contract path, address, and Abscan API key with your own.If successful, the output should look similar to the below output, and you can view your contract on a block explorer.
Deployer: 0x9C073184e74Af6D10DF575e724DC4712D98976aC
Deployed to: 0x85717893A18F255285AB48d7bE245ddcD047dEAE
Transaction hash: 0x2a4c7c32f26b078d080836b247db3e6c7d0216458a834cfb8362a2ac84e68d9f

Contract successfully verified