How to Verify Your Smart Contract Source Code on Etherscan?

Understanding Smart Contract Verification

1. Smart contract verification on Etherscan confirms that the deployed bytecode matches the human-readable source code submitted by the developer.

2. This process enables transparency, allowing users and auditors to inspect logic, identify potential vulnerabilities, and verify intended functionality.

3. Without verification, the contract appears as unverified bytecode—obscuring its behavior and reducing trust among participants in decentralized applications.

4. Verification does not imply security or correctness; it only attests to source-code–bytecode correspondence.

5. The verification step is mandatory for listings on many DeFi dashboards, token explorers, and third-party analytics platforms tied to Ethereum-based ecosystems.

Prerequisites for Successful Verification

1. You must have access to the exact Solidity compiler version used during deployment—down to the patch level (e.g., v0.8.19+commit.7dd6d404).

2. Optimization settings—including the number of runs—must be identical to those configured in the original compilation environment.

3. The constructor arguments must be ABI-encoded correctly and appended to the deployed bytecode if the contract was deployed with parameters.

4. All imported dependencies—such as OpenZeppelin libraries or custom interfaces—must be flattened or provided in a single file or via multi-file upload with proper path mapping.

5. The contract name must match the one defined in the source file and used during deployment, including case sensitivity and underscores.

Step-by-Step Manual Verification Process

1. Navigate to the contract’s Etherscan page using its deployed address and click “Code” tab, then “Verify and Publish”.

2. Select the correct compiler version from the dropdown menu—mismatched versions will cause immediate failure.

3. Choose the appropriate license type; selecting “None” or an incompatible license may trigger warnings or rejection.

4. Paste the full, flattened source code into the editor or use the “Upload Files” option for multi-file contracts with accurate directory structure.

5. Input the constructor arguments in ABI-encoded hex format if applicable—tools like Remix IDE or ethers.js utilities assist in generating this value.

Common Verification Failures and Fixes

1. “Compiler version mismatch” errors occur when the selected Etherscan version differs from the one used at deployment—even minor differences like +commit hashes matter.

2. “Invalid constructor arguments” appear when the hex string is malformed, too short, or contains non-hex characters; always validate using ABI coder tools.

3. “License identifier not found” arises when SPDX tags are missing or misformatted—include // SPDX-License-Identifier: MIT at the top of every source file.

4. “Source code contains syntax errors” indicates incomplete flattening or unresolved imports—use solc-flattener or Hardhat’s built-in flattening task before submission.

Frequently Asked Questions

Q: Can I verify a contract deployed via a factory pattern?A: Yes—if you know the exact bytecode and constructor arguments passed to the factory’s create function. You must verify the child contract address separately, not the factory itself.

Q: Does Etherscan support Vyper or other languages?A: Etherscan supports Vyper verification but requires selecting the correct Vyper compiler version and providing the compiled JSON output alongside source code.

Q: What happens if I lose my original compilation settings?A: You can often recover them using tools like sourcify.dev or by recompiling with build artifacts from Hardhat or Foundry cache directories.

Q: Is verification possible for contracts deployed on L2 chains like Arbitrum or Optimism?A: Yes—each Etherscan-branded explorer (e.g., arbiscan.io, optimismscan.io) offers identical verification flows tailored to their respective networks.