Token Analyzer Skill

Purpose

Analyze ERC20/ERC721/ERC1155 token implementations for non-standard behavior, fee-on-transfer mechanics, rebasing logic, and integration risks.

Detection Capabilities

• Fee-on-transfer tokens (deflationary)
• Rebasing tokens (elastic supply)
• Tokens with blacklists/whitelists (USDC, USDT)
• Tokens with pausable transfers
• Tokens with max transaction limits
• Missing return values (USDT-style)
• Tokens with callback hooks (ERC777)
• Tokens returning false instead of reverting
• Approval race conditions
• Double-entry point tokens (tusd-style)
• Tokens with admin mint/burn

Why This Matters

Over $500M has been lost due to protocol assumptions about "standard" ERC20 behavior. Most tokens deviate from the standard in subtle ways that break DeFi integrations.

Resources

• Integration Patterns
• Weird Tokens List

Workflows

• Token Analysis

Prerequisites

Token analysis requires the Solidity Scanner for EVM token implementations. Non-EVM token analysis may require chain-specific scanner skills.

Validation

To verify token detection capabilities, test against known weird tokens:

// Example: Detecting fee-on-transfer behavior
interface IERC20 {
    function transfer(address to, uint256 amount) external returns (bool);
    function balanceOf(address account) external view returns (uint256);
}

// Detection pattern: balance before/after comparison
uint256 balanceBefore = token.balanceOf(address(this));
token.transferFrom(sender, address(this), amount);
uint256 received = token.balanceOf(address(this)) - balanceBefore;
// If received < amount → fee-on-transfer detected
assert(received == amount); // Will fail for deflationary tokens

# Validate token categorization
def test_weird_token_detection():
    categories = ['fee-on-transfer', 'rebasing', 'blacklist', 'pausable', 'missing-return']
    for cat in categories:
        assert token_analyzer.can_detect(cat), f"Missing detection: {cat}"
    print("All token categories verified")

# Token risk scoring
token: USDT
risks:
  - missing_return_value: true   # Does not return bool
  - blacklist: true              # Admin can freeze addresses
  - pausable: true               # Admin can pause transfers
risk_level: medium

Behavior Guidelines

• Token analysis MUST check all integration points where external tokens are received
• Fee-on-transfer detection is required for any DeFi protocol handling arbitrary ERC20s
• Rebasing token checks may optionally be skipped if the protocol explicitly disallows them
• Missing return value handling ALWAYS needs verification (USDT compatibility)