eth_chainId on Ethereum

Everything below was measured on 2026-10-13 by calling eth_chainId on Ethereum through the same endpoint customers use, and is re-measured weekly.

What eth_chainId does

Returns the chain ID (EIP-155) as a hex string. Wallets and libraries check it before signing, and the signature commits to it, so a transaction signed for one chain cannot be replayed on another.

Example request

curl -s https://rpc.swiftnodes.io/rpc/eth?key=YOUR_API_KEY \
  -X POST -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"eth_chainId","params":[]}'

// Check you are on Ethereum before signing
import { createPublicClient, http } from "viem";

const client = createPublicClient({
  transport: http("https://rpc.swiftnodes.io/rpc/eth?key=YOUR_API_KEY"),
});

const id = await client.getChainId(); // 1
if (id !== 1) throw new Error(`wrong chain: ${id}`);

// Add Ethereum to a browser wallet
await window.ethereum.request({
  method: "wallet_addEthereumChain",
  params: [{
    chainId: "0x1",
    chainName: "Ethereum",
    nativeCurrency: { name: "ETH", symbol: "ETH", decimals: 18 },
    rpcUrls: ["https://rpc.swiftnodes.io/rpc/eth?key=YOUR_API_KEY"],
  }],
});

Other methods on Ethereum

• eth_blockNumberSupported
• eth_getBalanceSupported
• eth_getBlockByNumberSupported
• eth_getTransactionByHashSupported
• eth_getTransactionReceiptSupported
• eth_callSupported
• eth_estimateGasSupported
• eth_gasPriceSupported
• eth_maxPriorityFeePerGasSupported
• eth_sendRawTransactionSupported
• eth_getTransactionCountSupported
• eth_getCodeSupported
• eth_subscribeSupported
• eth_getLogsSupported
• eth_getBlockReceiptsSupported
• eth_feeHistorySupported
• eth_getProofSupported
• eth_createAccessListSupported
• debug_traceCallSupported
• trace_blockSupported
• trace_transactionSupported

eth_chainId on other chains

• Base
• Arbitrum
• Optimism
• Polygon
• BNB Smart Chain
• Avalanche
• Sonic
• Linea
• Scroll
• zkSync Era
• Blast
• Mantle
• Gnosis
• Celo
• Berachain
• Monad
• Unichain
• Kaia
• PulseChain
• World Chain
• Ronin
• Abstract
• ApeChain
• MegaETH
• Fantom
• Lisk
• Hemi
• X Layer
• BOB
• Plasma
• Fraxtal
• Zora
• Story
• Soneium
• Sei
• Hyperliquid
• Taiko
• Morph
• Ink
• Katana
• Ethereum Classic
• opBNB
• Mode
• Flare
• Core
• Chiliz
• Telos EVM
• Tempo
• Cronos
• Manta Pacific
• Shibarium
• Boba Network
• Arbitrum Nova
• Immutable zkEVM

Frequently asked questions