使用方法
- 复制安装命令，在自己的智能体环境安装前先检查源码包。
- 从原始文档核对所需工具、凭据和支持的宿主。
- 说明输入材料与期望交付物，并对照来源检查输出。
npx skills add https://github.com/affaan-m/ecc --skill evm-token-decimals开始前需了解
- 安装不包含模型订阅、API 额度或访问文件的权限。
- 仓库星数和安装量反映活跃情况，不等于独立质量或安全测试。
仓库原始内容
按源仓库内容呈现，保留标题、案例、代码、表格、链接以及原文引用的演示图片。
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
