Claude Code Agent: Smart Contract Auditor — Web3 Security

What it is

Smart Contract Auditor is a specialized Claude Code agent for blockchain and Web3 security tasks. It conducts security assessments of Solidity smart contracts, detecting vulnerabilities like reentrancy attacks, integer overflow, access control issues, flash loan exploits, and MEV attack vectors. The agent uses a systematic approach combining automated scanning with manual inspection for business logic flaws.

This agent targets Solidity developers and security researchers who need automated vulnerability detection before deploying contracts to mainnet. It integrates with static analysis tools like Slither, Mythril, and Semgrep.

How it saves time or tokens

Manual smart contract auditing requires deep expertise and hours of line-by-line review. This agent automates the first pass, identifying common vulnerability patterns and flagging suspicious code sections. The token estimate is approximately 500 tokens for the agent configuration.

The agent generates structured audit reports with severity classifications, so development teams can prioritize fixes by impact rather than reviewing findings in random order.

How to use

1. Install the agent from Claude Code Templates:

npx claude-code-templates@latest --agent blockchain-web3/smart-contract-auditor --yes

1. The agent activates automatically when Claude Code detects Solidity files or blockchain-related tasks.

1. Ask the agent to audit a contract:

Audit the Vault.sol contract for security vulnerabilities.
Focus on reentrancy, access control, and economic attack vectors.

Example

The agent produces structured findings like this:

Audit Report: Vault.sol

Critical

• Reentrancy in withdraw(): External call before state update

on line 45. Move the balance update before the transfer.

High

• Missing access control on setFee(): Any address can change

the protocol fee. Add onlyOwner modifier.

Medium

• Unchecked return value: transferFrom on line 78 does not

check the boolean return. Use SafeERC20.safeTransferFrom.

Gas Optimization

• Storage reads in loop: balances[msg.sender] read 3 times

in processRewards(). Cache in a local variable.

The agent can also generate proof-of-concept exploit code:

// Reentrancy exploit PoC

contract Exploit {

Vault public vault;

constructor(address _vault) {

vault = Vault(_vault);

}

function attack() external payable {

vault.deposit{value: msg.value}();

vault.withdraw();

}

receive() external payable {

if (address(vault).balance >= 1 ether) {

vault.withdraw();

}

}

}

Related on TokRepo

• AI Tools for Security -- Security scanning and audit tools
• AI Tools for Coding -- Developer productivity agents and tools

Common pitfalls

• Automated auditing catches common patterns but misses business logic vulnerabilities. Always pair automated scanning with manual review of economic incentives and edge cases.
• The agent works with Solidity contracts. Vyper, Cairo, and Move contracts require different tooling and analysis approaches.
• Static analysis tools (Slither, Mythril) need to be installed separately. The agent integrates with them but does not install them. Run pip install slither-analyzer and pip install mythril before using those features.