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. If verified, the code tab will display a green checkmark.
Selecting the Code tab will provide additional information about your contract.

Resources

Learn more about plugin configs, troubleshooting etc. at https://hardhat.org/plugins/nomiclabs-hardhat-etherscan.html
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Get Started
1) Install Hardhat
2) Create a project
3) Install plugin
4) Add plugin reference to config file
Config File
Add an Unsupported Network
Deploy and Verify
Deploy
Verify
Confirm Verification on BlockScout
Resources