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Contract verification is essential for transparency and allows users to interact with deployed contracts through block explorers. This guide covers verification for both Etherscan-based explorers and Tenderly.

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Prerequisites

Before verifying contracts, ensure you have:
  • Node.js and yarn installed
  • Cloned the CoW Protocol contracts repository
  • Deployed contracts on your target network
  • Appropriate API keys for verification services

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Etherscan Verification

Etherscan verification works for all Etherscan-based block explorers including:

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Setup API Key

First, obtain an API key from the relevant block explorer and set it as an environment variable: 
export ETHERSCAN_API_KEY=your_api_key_here
Most Etherscan-based explorers use the same API key variable ETHERSCAN_API_KEY. Check your Hardhat configuration for network-specific variable names.

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Verify All Deployed Contracts

To verify all contracts deployed on a specific network: 
export ETHERSCAN_API_KEY=<Your Key>
NETWORK='mainnet'  # or 'xdai', 'arbitrumOne', 'optimism', etc.
yarn verify:etherscan --network $NETWORK
The following network names are recognized by the verification scripts:
  • mainnet - Ethereum Mainnet
  • xdai - Gnosis Chain
  • arbitrumOne - Arbitrum One
  • optimism - Optimism
  • polygon - Polygon
  • bsc - BNB Smart Chain
  • base - Base
  • avalanche - Avalanche C-Chain
  • sepolia - Sepolia Testnet
  • goerli - Goerli Testnet (deprecated)
  • rinkeby - Rinkeby Testnet (deprecated)

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Verify Individual Contracts

Some contracts, like the VaultRelayer, are deployed indirectly and require manual verification with constructor arguments.

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Verify GPv2VaultRelayer

The VaultRelayer contract requires the Balancer Vault address as a constructor argument: 
NETWORK='mainnet'
VAULT_RELAYER_ADDRESS='0xC92E8bdf79f0507f65a392b0ab4667716BFE0110'
BALANCER_VAULT='0xBA12222222228d8Ba445958a75a0704d566BF2C8'

npx hardhat verify --network $NETWORK $VAULT_RELAYER_ADDRESS $BALANCER_VAULT
The Balancer Vault address (0xBA12222222228d8Ba445958a75a0704d566BF2C8) is consistent across most networks.

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Verify Custom Contracts

For other contracts with constructor arguments: 
npx hardhat verify --network $NETWORK CONTRACT_ADDRESS "constructor_arg_1" "constructor_arg_2"

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Verification Example

Complete example for Ethereum mainnet: 
# Set network and API key
export NETWORK='mainnet'
export ETHERSCAN_API_KEY='ABC123...'

# Verify all contracts
yarn verify:etherscan --network $NETWORK

# Manually verify VaultRelayer if needed
npx hardhat verify --network $NETWORK \
  0xC92E8bdf79f0507f65a392b0ab4667716BFE0110 \
  0xBA12222222228d8Ba445958a75a0704d566BF2C8

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Tenderly Verification

Tenderly provides advanced debugging and monitoring capabilities. Verify contracts on Tenderly for enhanced development experience.

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Setup Tenderly

First, configure Tenderly credentials: 
# Login to Tenderly CLI
tenderly login

# Or set credentials directly
export TENDERLY_USERNAME=your_username
export TENDERLY_PROJECT=your_project

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Verify All Contracts

Verify all deployed contracts on a network: 
NETWORK='mainnet'
yarn verify:tenderly --network $NETWORK

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Verify Individual Contract

Verify a specific contract by name and address: 
NETWORK='mainnet'
CONTRACT_NAME='GPv2Settlement'
CONTRACT_ADDRESS='0x9008D19f58AAbD9eD0D60971565AA8510560ab41'

npx hardhat tenderly:verify --network $NETWORK $CONTRACT_NAME=$CONTRACT_ADDRESS
Use these contract names when verifying on Tenderly:
  • GPv2Settlement
  • GPv2AllowListAuthentication
  • GPv2VaultRelayer
  • GPv2AllowListAuthentication_Implementation
  • GPv2AllowListAuthentication_Proxy

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Verify Multiple Contracts

You can verify multiple contracts in a single command: 
npx hardhat tenderly:verify --network $NETWORK \
  GPv2Settlement=0x9008D19f58AAbD9eD0D60971565AA8510560ab41 \
  GPv2AllowListAuthentication=0x2c4c28DDBdAc9C5E7055b4C863b72eA0149D8aFE

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Verification Best Practices

Important Considerations:
  1. Always verify contracts immediately after deployment
  2. Keep deployment artifacts in version control
  3. Document constructor arguments for manual verification
  4. Verify on multiple explorers for redundancy
  5. Test verification scripts before mainnet deployment

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Verification Checklist

Before considering verification complete:
  • All core contracts verified on primary block explorer
  • VaultRelayer contract manually verified with correct constructor args
  • Proxy and implementation contracts both verified
  • Contract source code matches repository
  • Compiler version and settings are correct
  • Constructor arguments are properly encoded
  • Verification status visible on block explorer

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Troubleshooting

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Common Issues

If a contract is already verified, you’ll see an error message. This is normal and means the contract is already accessible on the block explorer.
Error: Contract source code already verified
No action needed - the contract is already verified.
If verification fails due to constructor arguments:
Error: Missing constructor arguments
Solution:
  1. Find the deployment transaction on the block explorer
  2. Extract constructor arguments from the transaction input data
  3. Provide them explicitly to the verify command
For GPv2Settlement, constructor arguments are:
[
  "0x2c4c28DDBdAc9C5E7055b4C863b72eA0149D8aFE", // authenticator
  "0xBA12222222228d8Ba445958a75a0704d566BF2C8"  // vault
]
If you see an API key error:
Error: Invalid API Key
Solution:
  1. Verify your API key is correct
  2. Ensure environment variable is properly set
  3. Check API key has not expired
  4. Confirm API key is for the correct network
If the network is not recognized:
Error: Network not found
Solution:
  1. Check hardhat.config.ts for supported networks
  2. Ensure network name matches configuration
  3. Verify RPC URL is accessible
  4. Check network is supported by the block explorer

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Automated Verification Pipeline

For CI/CD integration, create a verification script: 
#!/bin/bash

set -e

NETWORK=${1:-"mainnet"}
ETHERSCAN_API_KEY=${2}

if [ -z "$ETHERSCAN_API_KEY" ]; then
  echo "Error: ETHERSCAN_API_KEY not provided"
  exit 1
fi

echo "Verifying contracts on $NETWORK..."

# Verify all contracts
yarn verify:etherscan --network $NETWORK

# Verify VaultRelayer separately
echo "Verifying VaultRelayer..."
npx hardhat verify --network $NETWORK \
  0xC92E8bdf79f0507f65a392b0ab4667716BFE0110 \
  0xBA12222222228d8Ba445958a75a0704d566BF2C8

echo "Verification complete!"

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Verification Status

Check verification status programmatically: 
const { ethers } = require('ethers');
const provider = new ethers.providers.EtherscanProvider(
  'mainnet',
  process.env.ETHERSCAN_API_KEY
);

async function checkVerification(address) {
  try {
    const code = await provider.getCode(address);
    console.log('Contract deployed:', code !== '0x');
    
    // Check on Etherscan API
    const url = `https://api.etherscan.io/api?module=contract&action=getsourcecode&address=${address}&apikey=${process.env.ETHERSCAN_API_KEY}`;
    const response = await fetch(url);
    const data = await response.json();
    
    console.log('Verified:', data.result[0].SourceCode !== '');
  } catch (error) {
    console.error('Error:', error.message);
  }
}

checkVerification('0x9008D19f58AAbD9eD0D60971565AA8510560ab41');

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