Evm Token Decimals

作者 affaan-mef648e01899ba3e8dc6371642deaaf64b4477775無授權條款275K 個星標收錄於 2026年10月9日更新於 2026年10月9日儲存庫4 天前更新

Prevent silent decimal mismatch bugs across EVM chains. Covers runtime decimal lookup, chain-aware caching, bridged-token precision drift, and safe normalization for bots, dashboards, and DeFi tools. Use when handling token amounts across EVM chains, or when a balance, price, or transfer amount is off by orders of magnitude.

僅含說明Software Development

AI 產生的概覽

指導如何正確讀取 EVM 各鏈上 ERC-20 代幣精度，避免靜默的小數位不匹配錯誤。

功能: 說明應在執行時查詢 ERC-20 代幣的 decimals()，而非假定固定值，並依鏈 ID 與代幣地址快取結果。提供 Python、TypeScript 與 Solidity 範例，涵蓋餘額讀取、精確小數運算、例外回退處理以及正規化為 18 位 WAD。也列出在跨鏈橋或包裝代幣變更後重新查詢精度等規則。
適用情境: 適用於讀取 ERC-20 餘額、依鏈上數量計算法幣價值、跨多條 EVM 鏈比較代幣數量，或處理跨鏈橋資產時。也適用於餘額、價格或轉帳金額出現數量級偏差的情況。
執行需求: 不附帶指令碼，僅為說明與程式碼範例。範例涉及 Python 的 web3 與 decimal、TypeScript 的 ethers、Solidity 以及 cast 命令列工具，並需要存取 EVM 鏈的 RPC。

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 Decimalfrom 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)

from decimal import Decimalfrom 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()

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 = 18

try:    decimals = contract.functions.decimals().call()except Exception:    logging.warning(        "decimals() reverted on %s (chain %s), defaulting to 18",        token_address,        chain_id,    )    decimals = 18

Log 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);}

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);}

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

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

來源與署名

來源：affaan-m/ECC位於skills/evm-token-decimals提交ef648e0

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Evm Token Decimals

EVM Token Decimals

When to Use

How It Works

Examples

Query decimals at runtime

Cache by chain and token

Handle odd tokens defensively

Normalize to 18-decimal WAD in Solidity

TypeScript with ethers

Quick on-chain check

Rules

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