RPC method

eth_chainId on Core

Supported on SwiftNodes

Everything below was measured on 2026-10-13 by calling eth_chainId on Core 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.

Core 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 Core a legacy transaction signed without a chain ID (pre-EIP-155). Its nodes refused it: "only replay-protected (EIP-155) transactions allowed over RPC". Sign with chain ID 1116; every mainstream library does this by default.

eth_chainId	0x45c (1,116)
net_version	1116

Example request

curl -s https://rpc.swiftnodes.io/rpc/core?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 Core before signing
import { createPublicClient, http } from "viem";

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

const id = await client.getChainId(); // 1116
if (id !== 1116) throw new Error(`wrong chain: ${id}`);

// Add Core to a browser wallet
await window.ethereum.request({
  method: "wallet_addEthereumChain",
  params: [{
    chainId: "0x45c",
    chainName: "Core",
    nativeCurrency: { name: "CORE", symbol: "CORE", decimals: 18 },
    rpcUrls: ["https://rpc.swiftnodes.io/rpc/core?key=YOUR_API_KEY"],
  }],
});

Other methods on Core

eth_chainId on other chains

Frequently asked questions

Does Core support eth_chainId?

Yes. eth_chainId answered on the SwiftNodes Core endpoint when our weekly probe called it through the customer path (2026-10-13).

What is the Core chain ID?

1116 in decimal, 0x45c in hex, as returned by eth_chainId on 2026-10-13.

How do I add Core to MetaMask?

Call wallet_addEthereumChain with chainId 0x45c, the native currency CORE with 18 decimals, and your RPC URL; the example on this page has the full object.

Core endpoints, live block height and WebSocket status are on the Core RPC page.

One key covers every chain we serve, and SwiftNodes has a free tier.