etherscan-verification

name	etherscan-verification
description	Verify smart contracts on Etherscan-compatible block explorers. This skill should be used when the user asks to "verify contract", "verify on etherscan", "verify on chain scan". Handles standard verification, Etherscan V2 API for unsupported chains on foundry, proxy patterns, and factory-created contracts.
version	0.1.0

Overview

Contract verification on Etherscan-compatible explorers using Foundry's forge verify-contract. Covers standard verification, unsupported chains via Etherscan V2 API, proxy patterns, and factory-created contracts.

When to Use

• Verify deployed smart contracts on Etherscan-compatible explorers
• Verify proxy contracts (ERC1967, UUPS)
• Verify factory-created contracts (CREATE2)
• Extract constructor arguments from deployment data

Prerequisites

Requirement	How to Get
Foundry ≥1.3.6	Run forge -V to check version
Contract address	From deployment broadcast or user
Chain ID	From explorer or network configuration
Explorer API key	From Etherscan account (works for V2 multi-chain)
Source code	Must match deployed bytecode exactly

Version Check

Before proceeding, verify Foundry version:

forge -V

Stop if version is below 1.3.6.

Verification Methods

Method 1: Standard (Native Support)

For chains Foundry supports natively:

FOUNDRY_PROFILE=optimized forge verify-contract \
  <CONTRACT_ADDRESS> \
  src/<Contract>.sol:<Contract> \
  --rpc-url <chain_name> \
  --verifier etherscan \
  --etherscan-api-key $ETHERSCAN_API_KEY \
  --watch

Method 2: Etherscan V2 API (Unsupported Chains on Foundry)

When Foundry shows "No known Etherscan API URL for chain X":

FOUNDRY_PROFILE=optimized forge verify-contract \
  <CONTRACT_ADDRESS> \
  src/<Contract>.sol:<Contract> \
  --verifier etherscan \
  --verifier-url "https://api.etherscan.io/v2/api?chainid=<CHAIN_ID>" \
  --etherscan-api-key $ETHERSCAN_API_KEY \
  --watch

Supported chains: https://docs.etherscan.io/supported-chains

Method 3: With Constructor Arguments

For contracts with constructor parameters:

FOUNDRY_PROFILE=optimized forge verify-contract \
  <CONTRACT_ADDRESS> \
  src/<Contract>.sol:<Contract> \
  --verifier etherscan \
  --verifier-url "https://api.etherscan.io/v2/api?chainid=<CHAIN_ID>" \
  --etherscan-api-key $ETHERSCAN_API_KEY \
  --constructor-args <ABI_ENCODED_ARGS> \
  --watch

Generate constructor args with cast abi-encode:

cast abi-encode "constructor(address,uint256)" 0x123... 1000

Special Cases

Reference: ./references/special-cases.md

Proxy Contracts

Verify implementation and proxy separately. See reference for ERC1967 pattern.

Factory-Created Contracts

Extract constructor args from broadcast initCode using scripts/extract_constructor_args.py.

Library Verification

For libraries, use full path:

src/libraries/<Library>.sol:<Library>

Troubleshooting

Reference: ./references/troubleshooting.md

Common Issues

Error	Cause	Solution
"No known Etherscan API URL"	Chain not in Foundry	Use --verifier-url with V2 API
"Bytecode does not match"	Compilation drift	Checkout deployment commit + reinstall deps
"Constructor args mismatch"	Wrong/missing args	Extract from broadcast or encode manually
"Already verified"	Previously verified	No action needed

Output

After successful verification:

• Contract source visible on explorer
• ABI available for interaction
• Constructor args decoded
• "Contract Source Code Verified" badge

Examples

Reference: ./references/examples.md for real-world verification examples from Monad deployment.