Hardhat Verification Plugin

Hardhat is a full-featured development environment for contract compilation, deployment and verification. The Hardhat Etherscan plugin supports contract verification on BlockScout.

Get Started

1) Install Hardhat

If you are starting from scratch, create an npm project by going to an empty folder, running npm init, and following the instructions. Recommend npm 7 or higher.

Once your project is ready:

npm instructions

npm install --save-dev hardhat

yarn instructions

yarn add --dev hardhat

2) Create a project

Run npx hardhat in your project folder and follow the instructions to create (more info here).

3) Install plugin

Install the hardhat-etherscan plugin (requires v3.0.0+).

npm

npm install --save-dev @nomiclabs/hardhat-etherscan

yarn

yarn add --dev @nomiclabs/hardhat-etherscan

4) Add plugin reference to config file

Add the following statement to your hardhat.config.js.

require("@nomiclabs/hardhat-etherscan");

If using TypeScript, add this to your hardhat.config.ts. More info on using typescript with hardhat available here.

import "@nomiclabs/hardhat-etherscan";

Config File

Your basic Hardhat config file (hardhat.config.js or hardhat.config.ts) will be setup to support the network you are working on. In this example we use the Sokol test network and a .js file.

Here we add an RPC url without an API key, however some value is still required. You can use any arbitrary string. More info.

If you prefer, you can migrate to hardhat-toolbox to use a plugin bundle.

require("@nomiclabs/hardhat-waffle");
require("@nomiclabs/hardhat-etherscan");
require('hardhat-deploy');

let secret = require("./secret");

module.exports = {
  solidity: "0.8.9",
  networks: {
    sokol: {
      url: 'https://sokol.poa.network/',
      accounts: [secret.key],
    }
  },
  etherscan: {
    // Your API key for Etherscan
    // Obtain one at https://etherscan.io/
    apiKey: "abc"
  }
};

Add an Unsupported Network

Some chains are not supported by the plugin (to check run npx hardhat verify --list-networks)

If your chain is not in the list, you can add a customChains object to the config file. It includes:

• chainID - Network chain ID

• apiURL - Block explorer API URL

• browserURL - Block explorer URL

Find an extensive list of ChainIDs at https://chainlist.org/.

For example, if Sokol were not in the default list, this is how it would be added to the config file. Note the network name in customChains must match the network name in the apiKey object.

etherscan: {
  apiKey: {
    sokol: "abc"
  },
  customChains: [
    {
      network: "sokol",
      chainId: 77,
      urls: {
        apiURL: "https://blockscout.com/poa/sokol/api",
        browserURL: "https://blockscout.com/poa/sokol"
      }
    }
  ]
}

Deploy and Verify

Deploy

D:\hard_hat>npx hardhat run scripts\deploy.js --network sokol
Contract deployed to: 0x8595e22825Ba499dB8C77C5c830c235D80f9C0fa

Verify

You can include constructor arguments with the verify task.

npx hardhat verify --network <network> DEPLOYED_CONTRACT_ADDRESS "Constructor argument 1"

Sokol example (no constructors).

D:\hard_hat>npx hardhat verify --network sokol 0x8595e22825Ba499dB8C77C5c830c235D80f9C0fa 
Nothing to compile
Compiling 1 file with 0.8.0
Successfully submitted source code for contract
contracts/test.sol:Foo at 0x8595e22825Ba499dB8C77C5c830c235D80f9C0fa
for verification on Etherscan. Waiting for verification result...

Successfully verified contract Foo on Etherscan.
https://blockscout.com/poa/sokol/address/0x8595e22825Ba499dB8C77C5c830c235D80f9C0fa#code

Note the verify task will not be listed in the available tasks lists at npx hardhat --config but should work as expected.

If not, check you have the minimum required version of the nomiclabs-hardhat-etherscan plugin (v3.0.0+) installed

Confirm Verification on BlockScout

Go to your BlockScout instance and paste the contract address into the search bar.

Scroll down to see verified status. A green checkmark ✅ means the contract is verified.

If your screen size is limited, you may need to click the 3 dots to view and click through to the contract.

Scroll down to see and interact with the contract code.

FAQ

I am using an OpenZeppelin upgrades plugin implementation and receive an error on proxy contract verification. What should I do?

Although you receive an error, the contracts should be verified during the previous steps and you can ignore. Check in the explorer to make sure the contracts have been verified.

Resources

Learn more about plugin configs, troubleshooting etc. at https://hardhat.org/plugins/nomiclabs-hardhat-etherscan.html