RPC method

eth_chainId on Base

Supported on SwiftNodes

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

Base 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 Base a legacy transaction signed without a chain ID (pre-EIP-155). Its nodes refused it: "error getting sender from raw transaction". Sign with chain ID 8453; every mainstream library does this by default.

eth_chainId	0x2105 (8,453)
net_version	8453

Example request

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

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

const id = await client.getChainId(); // 8453
if (id !== 8453) throw new Error(`wrong chain: ${id}`);

// Add Base to a browser wallet
await window.ethereum.request({
  method: "wallet_addEthereumChain",
  params: [{
    chainId: "0x2105",
    chainName: "Base",
    nativeCurrency: { name: "ETH", symbol: "ETH", decimals: 18 },
    rpcUrls: ["https://rpc.swiftnodes.io/rpc/base?key=YOUR_API_KEY"],
  }],
});

Other methods on Base

eth_chainId on other chains

Frequently asked questions

Does Base support eth_chainId?

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

What is the Base chain ID?

8453 in decimal, 0x2105 in hex, as returned by eth_chainId on 2026-10-13.

How do I add Base to MetaMask?

Call wallet_addEthereumChain with chainId 0x2105, the native currency ETH with 18 decimals, and your RPC URL; the example on this page has the full object.

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

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