Contract verification allows users and developers to view and interact with your contract source code on block explorers like Etherscan.
Automatic Verification
The easiest way to verify contracts is during deployment by adding the --verify flag to your Forge script command.
During Deployment
forge script script/DeployAllContracts.s.sol:DeployAllContracts \
--rpc-url $ETH_RPC_URL \
--private-key $PRIVATE_KEY \
--broadcast \
--verify
Ensure the ETHERSCAN_API_KEY environment variable is set before using the --verify flag.
Manual Verification
If automatic verification fails or you need to verify an already deployed contract, use the forge verify-contract command.
Prerequisites
Set environment variables
export CHAIN_ID=1 # Target network chain ID
export ETHERSCAN_API_KEY=your_api_key_here
Identify contract addresses
Find the deployed contract addresses in networks.json or from your deployment output.
Verify FlashLoanRouter
The FlashLoanRouter is initialized with the CoW Settlement contract address (0x9008D19f58AAbD9eD0D60971565AA8510560ab41).
forge verify-contract \
0x9da8B48441583a2b93e2eF8213aAD0EC0b392C69 \
src/FlashLoanRouter.sol:FlashLoanRouter \
--chain-id $CHAIN_ID \
--etherscan-api-key $ETHERSCAN_API_KEY \
--constructor-args $(cast abi-encode "constructor(address)" 0x9008D19f58AAbD9eD0D60971565AA8510560ab41)
The constructor argument is the CoW Settlement contract address, which is consistent across all supported networks.
Verify AaveBorrower
The AaveBorrower is initialized with the FlashLoanRouter address.
forge verify-contract \
0x7d9C4DeE56933151Bc5C909cfe09DEf0d315CB4A \
src/AaveBorrower.sol:AaveBorrower \
--chain-id $CHAIN_ID \
--etherscan-api-key $ETHERSCAN_API_KEY \
--constructor-args $(cast abi-encode "constructor(address)" 0x9da8B48441583a2b93e2eF8213aAD0EC0b392C69)
Verify ERC3156Borrower
The ERC3156Borrower is also initialized with the FlashLoanRouter address.
forge verify-contract \
0x47d71b4B3336AB2729436186C216955F3C27cD04 \
src/ERC3156Borrower.sol:ERC3156Borrower \
--chain-id $CHAIN_ID \
--etherscan-api-key $ETHERSCAN_API_KEY \
--constructor-args $(cast abi-encode "constructor(address)" 0x9da8B48441583a2b93e2eF8213aAD0EC0b392C69)
Understanding Constructor Arguments
The cast abi-encode command encodes constructor arguments in the format expected by Etherscan.
Syntax
cast abi-encode "constructor(type1,type2,...)" arg1 arg2 ...
Examples
# For contracts with single address parameter
cast abi-encode "constructor(address)" 0x9da8B48441583a2b93e2eF8213aAD0EC0b392C69
Network-Specific API Keys
Different networks require different API keys:
| Network | Explorer | API Key Environment Variable |
|---|
| Ethereum | Etherscan | ETHERSCAN_API_KEY |
| Polygon | Polygonscan | POLYGONSCAN_API_KEY |
| Arbitrum | Arbiscan | ARBISCAN_API_KEY |
| Optimism | Optimistic Etherscan | OPTIMISM_API_KEY |
| Base | Basescan | BASESCAN_API_KEY |
| BSC | BscScan | BSCSCAN_API_KEY |
| Avalanche | Snowtrace | SNOWTRACE_API_KEY |
| Gnosis | Gnosisscan | GNOSISSCAN_API_KEY |
| Linea | Lineascan | LINEASCAN_API_KEY |
Most explorers use the same API key infrastructure. Register at the respective explorer website to obtain your API key.
Verification Status
After running the verification command, you’ll see one of these outputs:
Start verifying contract `0x9da8B48441583a2b93e2eF8213aAD0EC0b392C69` deployed on mainnet
Submitting verification for [src/FlashLoanRouter.sol:FlashLoanRouter] "0x9da8B48441583a2b93e2eF8213aAD0EC0b392C69".
Submitted contract for verification:
Response: `OK`
GUID: `abc123...`
URL: https://etherscan.io/address/0x9da8B48441583a2b93e2eF8213aAD0EC0b392C69
Contract verification status:
Response: `OK`
Details: `Pass - Verified`
Contract source code already verified
Error: Verification failed
Response: `NOTOK`
Details: `Error message here`
- Incorrect constructor arguments
- Wrong compiler version or settings
- Invalid API key
- Network issues
See troubleshooting section below.Troubleshooting
Constructor argument mismatch
Ensure you’re using the correct addresses for constructor arguments:
- FlashLoanRouter: Uses CoW Settlement address
0x9008D19f58AAbD9eD0D60971565AA8510560ab41
- Borrower contracts: Use FlashLoanRouter address
0x9da8B48441583a2b93e2eF8213aAD0EC0b392C69
Verify addresses in networks.json for the specific network. Compiler version mismatch
The contracts are compiled with specific settings from foundry.toml:solc = "0.8.28"
evm_version = "cancun"
optimizer = true
optimizer_runs = 1000000
Block explorer APIs have rate limits. If you encounter rate limiting:
- Wait a few minutes before retrying
- Verify contracts sequentially, not in parallel
- Check your API key tier for rate limit details
Verify your API key is:
- Correctly set in environment variables
- Valid and not expired
- For the correct network (e.g., mainnet vs testnet)
- Has verification permissions enabled
Verify Multiple Contracts
To verify all three contracts sequentially:
#!/bin/bash
source .env
echo "Verifying FlashLoanRouter..."
forge verify-contract \
0x9da8B48441583a2b93e2eF8213aAD0EC0b392C69 \
src/FlashLoanRouter.sol:FlashLoanRouter \
--chain-id $CHAIN_ID \
--etherscan-api-key $ETHERSCAN_API_KEY \
--constructor-args $(cast abi-encode "constructor(address)" 0x9008D19f58AAbD9eD0D60971565AA8510560ab41)
echo "Verifying AaveBorrower..."
forge verify-contract \
0x7d9C4DeE56933151Bc5C909cfe09DEf0d315CB4A \
src/AaveBorrower.sol:AaveBorrower \
--chain-id $CHAIN_ID \
--etherscan-api-key $ETHERSCAN_API_KEY \
--constructor-args $(cast abi-encode "constructor(address)" 0x9da8B48441583a2b93e2eF8213aAD0EC0b392C69)
echo "Verifying ERC3156Borrower..."
forge verify-contract \
0x47d71b4B3336AB2729436186C216955F3C27cD04 \
src/ERC3156Borrower.sol:ERC3156Borrower \
--chain-id $CHAIN_ID \
--etherscan-api-key $ETHERSCAN_API_KEY \
--constructor-args $(cast abi-encode "constructor(address)" 0x9da8B48441583a2b93e2eF8213aAD0EC0b392C69)
echo "Verification complete!"
Make the script executable with chmod +x verify-all.sh before running.
Next Steps
