eth_chainId

eth_chainId returns the EIP-155 chain ID of the network the endpoint is serving. For Base — Coinbase's OP Stack rollup that uses ETH for gas — the answer at https://base.therpc.io/YOUR_API_KEY is 0x2105, which is decimal 8453. That number is the canonical identifier you embed in signed transactions so a payload meant for Base mainnet can never be replayed on Ethereum L1 or any other chain. It takes no parameters and costs a single CU.

Use cases

• Pre-condition check before signing or submitting — confirm the wallet is actually on Base (0x2105) and not Ethereum or another OP Stack chain.
• Combine with eth_blockNumber for a full "alive and on the right chain" probe of your Base endpoint in one health check.
• Select the correct contract address for a multi-chain deployment by keying off the returned 8453 value.
• Guard against cross-chain replay by pinning the chain ID into every EIP-155 signature you build for Base.

Parameters

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Response

Example request

1curl https://base.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H "Content-Type: application/json" \
4  -d '{
5    "jsonrpc": "2.0",
6    "method": "eth_chainId",
7    "params": [],
8    "id": 1
9  }'

Try it live in the Base playground.

Errors & troubleshooting

Common pitfalls

• Don't confuse this with net_version, which returns the network ID as a decimal string; on Base both happen to map to 8453, but treat them as separate concepts and use eth_chainId for EIP-155 signing.
• The result is a hex string ("0x2105"); compare with BigInt(result) === 8453n rather than string equality to avoid casing or zero-padding bugs.

Supported networks

• Mainnet — Chain ID: 8453
• Sepolia — Chain ID: 84532

See also

• eth_blockNumber
• net_version

1curl https://base.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H 'Content-Type: application/json' \
4  -d '{"jsonrpc":"2.0","id":1,"method":"eth_chainId","params":[]}'