eth_chainId on opBNB
Everything below was measured on 2026-10-13 by calling eth_chainId on opBNB 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.
opBNB chain ID, as measured
net_version returns the same number as decimal text. Older tools read net_version; use eth_chainId, which is the value signatures commit to.
We sent opBNB a legacy transaction signed without a chain ID (pre-EIP-155). Its nodes did not reject it for that: the answer was about the empty balance ("insufficient funds for gas * price + value: balance 0, tx cost 47690271946, overshot 47690271946"). Unprotected transactions are accepted at the RPC, so replay protection depends on your wallet signing with the chain ID.
| eth_chainId | 0xcc (204) |
|---|---|
| net_version | 204 |
Example request
curl -s https://rpc.swiftnodes.io/rpc/opbnb?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 opBNB before signing
import { createPublicClient, http } from "viem";
const client = createPublicClient({
transport: http("https://rpc.swiftnodes.io/rpc/opbnb?key=YOUR_API_KEY"),
});
const id = await client.getChainId(); // 204
if (id !== 204) throw new Error(`wrong chain: ${id}`);
// Add opBNB to a browser wallet
await window.ethereum.request({
method: "wallet_addEthereumChain",
params: [{
chainId: "0xcc",
chainName: "opBNB",
nativeCurrency: { name: "BNB", symbol: "BNB", decimals: 18 },
rpcUrls: ["https://rpc.swiftnodes.io/rpc/opbnb?key=YOUR_API_KEY"],
}],
});Other methods on opBNB
- 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_transactionNot available
eth_chainId on other chains
- Ethereum
- 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
- Mode
- Flare
- Core
- Chiliz
- Telos EVM
- Tempo
- Cronos
- Manta Pacific
- Shibarium
- Boba Network
- Arbitrum Nova
- Immutable zkEVM
Frequently asked questions
Does opBNB support eth_chainId?
Yes. eth_chainId answered on the SwiftNodes opBNB endpoint when our weekly probe called it through the customer path (2026-10-13).
What is the opBNB chain ID?
204 in decimal, 0xcc in hex, as returned by eth_chainId on 2026-10-13.
How do I add opBNB to MetaMask?
Call wallet_addEthereumChain with chainId 0xcc, the native currency BNB with 18 decimals, and your RPC URL; the example on this page has the full object.
opBNB endpoints, live block height and WebSocket status are on the opBNB RPC page.
One key covers every chain we serve, and SwiftNodes has a free tier.