Como usar
- Copie o comando e verifique o pacote antes de instalar no seu ambiente de agente.
- Consulte no original as ferramentas, credenciais e ambientes necessários.
- Descreva os dados de entrada e a entrega esperada; confira a saída com as fontes.
npx skills add https://github.com/affaan-m/ecc --skill evm-token-decimalsAntes de começar
- A instalação não inclui assinatura de modelo, franquia API ou acesso aos seus arquivos.
- Estrelas e instalações indicam atividade, não um teste independente de qualidade ou segurança.
Documento original do Skill
Renderizado do repositório de origem, preservando títulos, exemplos, código, tabelas, links e imagens.
EVM Token Decimals
Silent decimal mismatches are one of the easiest ways to ship balances or USD values that are off by orders of magnitude without throwing an error.
When to Use
- Reading ERC-20 balances in Python, TypeScript, or Solidity
- Calculating fiat values from on-chain balances
- Comparing token amounts across multiple EVM chains
- Handling bridged assets
- Building portfolio trackers, bots, or aggregators
How It Works
Never assume stablecoins use the same decimals everywhere. Query decimals() at runtime, cache by (chain_id, token_address), and use decimal-safe math for value calculations.
Examples
Query decimals at runtime
python
from decimal import Decimal
from web3 import Web3
ERC20_ABI = [
{"name": "decimals", "type": "function", "inputs": [],
"outputs": [{"type": "uint8"}], "stateMutability": "view"},
{"name": "balanceOf", "type": "function",
"inputs": [{"name": "account", "type": "address"}],
"outputs": [{"type": "uint256"}], "stateMutability": "view"},
]
def get_token_balance(w3: Web3, token_address: str, wallet: str) -> Decimal:
contract = w3.eth.contract(
address=Web3.to_checksum_address(token_address),
abi=ERC20_ABI,
)
decimals = contract.functions.decimals().call()
raw = contract.functions.balanceOf(Web3.to_checksum_address(wallet)).call()
return Decimal(raw) / Decimal(10 ** decimals)Do not hardcode 1_000_000 because a symbol usually has 6 decimals somewhere else.
Cache by chain and token
python
from functools import lru_cache
@lru_cache(maxsize=512)
def get_decimals(chain_id: int, token_address: str) -> int:
w3 = get_web3_for_chain(chain_id)
contract = w3.eth.contract(
address=Web3.to_checksum_address(token_address),
abi=ERC20_ABI,
)
return contract.functions.decimals().call()Handle odd tokens defensively
python
try:
decimals = contract.functions.decimals().call()
except Exception:
logging.warning(
"decimals() reverted on %s (chain %s), defaulting to 18",
token_address,
chain_id,
)
decimals = 18Log the fallback and keep it visible. Old or non-standard tokens still exist.
Normalize to 18-decimal WAD in Solidity
solidity
interface IERC20Metadata {
function decimals() external view returns (uint8);
}
function normalizeToWad(address token, uint256 amount) internal view returns (uint256) {
uint8 d = IERC20Metadata(token).decimals();
if (d == 18) return amount;
if (d < 18) return amount * 10 ** (18 - d);
return amount / 10 ** (d - 18);
}TypeScript with ethers
typescript
import { Contract, formatUnits } from 'ethers';
const ERC20_ABI = [
'function decimals() view returns (uint8)',
'function balanceOf(address) view returns (uint256)',
];
async function getBalance(provider: any, tokenAddress: string, wallet: string): Promise<string> {
const token = new Contract(tokenAddress, ERC20_ABI, provider);
const [decimals, raw] = await Promise.all([
token.decimals(),
token.balanceOf(wallet),
]);
return formatUnits(raw, decimals);
}Quick on-chain check
bash
cast call <token_address> "decimals()(uint8)" --rpc-url <rpc>Rules
- Always query
decimals()at runtime - Cache by chain plus token address, not symbol
- Use
Decimal,BigInt, or equivalent exact math, not float - Re-query decimals after bridging or wrapper changes
- Normalize internal accounting consistently before comparison or pricing
