Verifying Smart Contracts

Scroll Alpha Testnet is now deprecated.

Please visit our new documentation for the Scroll Sepolia Testnet at https://docs.scroll.io/

After deploying your smart contracts, it's important to verify your code on our block explorer. This can be done in an automated way using your developer tooling or using Blockscout's Web UI.

Our Blockscout instance currently has inconsistent behavior in verifying contracts with Foundry. We're working on a fix, along with other stability improvements. Don't hesitate to come ask for help on Discord though.

Using Developer Tools

Most smart contract tooling has plugins for verifying your contracts easily on Etherscan. Blockscout supports Etherscan's contract verification APIs, and it's straight forward to use these tools with the Scroll Alpha Testnet.

Hardhat

First, modify hardhat.config.ts to point to Scroll's RPC and blockscout.scroll.io/api. A dummy apyKey value is required, but anything works for its value.

...

const config: HardhatUserConfig = {
  ...
  networks: {
    scrollAlpha: {
      url: 'https://alpha-rpc.scroll.io/l2' || '',
      accounts:
        process.env.PRIVATE_KEY !== undefined ? [process.env.PRIVATE_KEY] : [],
    },
  },
  etherscan: {
    apiKey: {
      scrollAlpha: 'abc',
    },
    customChains: [
      {
        network: 'scrollAlpha',
        chainId: 534353,
        urls: {
          apiURL: 'https://blockscout.scroll.io/api',
          browserURL: 'https://blockscout.scroll.io/',
        },
      },
    ],
  },
}

...

Now you can verify the smart contract by running the following command.

npx hardhat verify --network scrollAlpha <contract address> <space separated constructor parameters>

For example, this how a smart contract that receives two uint parameters in the constructor would look like.

npx hardhat verify --network scrollAlpha 0xD9880690bd717189cC3Fbe7B9020F27fae7Ac76F 123 456

You may receive an error stating etherscan.apiKey.trim is not a function . If so, you need to update @nomiclabs/hardhat-etherscan to be able to support custom chains. Try running npm update @nomiclabs/hardhat-etherscan

Foundry

When using Foundry, the verify-contract helps us verifying contracts.

forge verify-contract <Contract Address> <Space separated params> <Solidity file>:<Contract name> --chain-id 534353 --verifier-url <https://blockscout.scroll.io/api> --verifier blockscout

For example, this what verifying a smart contract that receives two uint parameters in the constructor looks like:

forge verify-contract 0xD9880690bd717189cC3Fbe7B9020F27fae7Ac76F 123 456 src/MyContract.sol:MyContract --chain-id 534353 --verifier-url <https://blockscout.scroll.io/api> --verifier blockscout

Please note that certain issues have been reported when executing verifying Smart Contracts from Foundry. In such cases, we recommend trying an alternative method as described on the foundry issues page.

Truffle

To verify contracts with Truffle, first install the truffle-plugin-verify plugin.

npm install -D truffle-plugin-verify

Then, enable the plugin and connect Scroll's Alpha Testnet using the RPC URL and Blockscout verification API.

module.exports = {
  plugins: ['truffle-plugin-verify'],
  networks: {
    scrollAlpha: {
      provider: () =>
        new HDWalletProvider(process.env.PRIVATE_KEY, 'https://alpha-rpc.scroll.io/l2'),
      network_id: '*',
      verify: {
        apiUrl: 'https://blockscout.scroll.io/api',
        apiKey: 'abc',
        explorerUrl: 'https://blockscout.scroll.io/',
      },
    },
    
...

After migrating our smart contract, we can verify it.

npx truffle run verify MyContract --network scrollAlpha

Using the Blockscout Web UI

Shorter contracts can be verified using Blockscout's Web UI. To do so, combine all your Solidity code into one single file, including all the imported libraries. Then, lookup the deployed contract on on Blockscout, then visit the "Code" tab and select "Verify & Publish". Follow the instructions to submit your code.

For a more in-depth guide, see Blockscount's official documentation on Verifying a Smart Contract.