Hardhatis a full-featured development environment for contract compilation, deployment and verification. The hardhat-verify plugin supports contract verification on BlockScout.

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Get Started

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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

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2) Create a project

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

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3) Install plugin

Install the hardhat-verify plugin npm 
npm install --save-dev @nomicfoundation/hardhat-verify
yarn 
yarn add --dev @nomicfoundation/hardhat-verify

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4) Add plugin reference to config file

Add the following statement to your hardhat.config.js. 
require("@nomicfoundation/hardhat-verify");
If using TypeScript, add this to your hardhat.config.ts. More info on using typescript with hardhat available here. 
import "@nomicfoundation/hardhat-verify";

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Config File and Unsupported Networks

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 Optimism Sepolia 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. In order to use Blockscout explorer for the verification, you have to specify the explorer details under a customChains object. 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, here we added Blockscout api endpoints for the Optimism Sepolia network to the config file. Note the network name in customChains must match the network name in the apiKey object. 
import { HardhatUserConfig } from "hardhat/config";
import "@nomicfoundation/hardhat-toolbox";
import "@nomicfoundation/hardhat-verify";

const PRIVATE_KEY = vars.get("PRIVATE_KEY");

const config: HardhatUserConfig = {
  solidity: "0.8.24",
  networks: {
    'optimism-sepolia': {
      url: 'https://sepolia.optimism.io',
      accounts: [PRIVATE_KEY],
    },
  },
  etherscan: {
    apiKey: {
      // Is not required by blockscout. Can be any non-empty string
      'optimism-sepolia': "abc"
    },
    customChains: [
      {
        network: "optimism-sepolia",
        chainId: 11155420,
        urls: {
          apiURL: "https://optimism-sepolia.blockscout.com/api",
          browserURL: "https://optimism-sepolia.blockscout.com/",
        }
      }
    ]
  },
  sourcify: {
    enabled: false
  }
};

export default config;

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Deploy and Verify

For deployment we will use Hardhat Ignition - built-in Hardhat deployment system.

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Deploy

> npx hardhat ignition deploy ./ignition/modules/Lock.ts --network optimism-sepolia
✔ Confirm deploy to network optimism-sepolia (11155420)? … yes
Compiled 1 Solidity file successfully (evm target: paris).
Hardhat Ignition 🚀

Deploying [ LockModule ]

Batch #1
  Executed LockModule#Lock

[ LockModule ] successfully deployed 🚀

Deployed Addresses

LockModule#Lock - 0xFE826b33e425f99ce962ACB91752DB41F302EFEA

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Verify

The plugin requires you to include constructor arguments with the verify task and ensures that they correspond to expected ABI signature. However, Blockscout ignores those arguments, so you may specify any values that correspond to the ABI. 
npx hardhat verify --network <network> DEPLOYED_CONTRACT_ADDRESS "Constructor argument 1"
Optimism Sepolia example. 
> npx hardhat verify --network optimism-sepolia 0xFE826b33e425f99ce962ACB91752DB41F302EFEA 1234
Successfully submitted source code for contract
contracts/Lock.sol:Lock at 0xFE826b33e425f99ce962ACB91752DB41F302EFEA
for verification on the block explorer. Waiting for verification result...

Successfully verified contract Lock on the block explorer.
https://optimism-sepolia.blockscout.com/address/0xFE826b33e425f99ce962ACB91752DB41F302EFEA#code

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Automatically verified contracts

Sometimes the contract may be automatically verified via Ethereum Bytecode Database service. In that case you may see the following response: 
The contract 0xFE826b33e425f99ce962ACB91752DB41F302EFEA has already been verified on Etherscan.
https://optimism-sepolia.blockscout.com/address/0xFE826b33e425f99ce962ACB91752DB41F302EFEA#code
In that case, you may try to enforce using --force flag*. It prevents Hardhat to check if the contract is already verified, and force it to send verification request anyway. Notice, that it is helpful only if the contract was automatically verified partially. That way, a new verification sources would be saved. If the contract was fully verified already, that just returns an error. 
npx hardhat verify --network <network> DEPLOYED_CONTRACT_ADDRESS "Constructor argument 1" --force

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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.

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Video example

Community video created by Carlos Rodriguez for the Soneium Minato testnet, but can be applicable to any chain.

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FAQ

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Resources

Learn more about plugin configs, troubleshooting etc. at https://hardhat.org/hardhat-runner/plugins/nomicfoundation-hardhat-verify