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POST
/
efb0a5eccd2caa5135eb54eba6f7f300
eth_chainId
curl --request POST \
  --url https://optimism-mainnet.core.chainstack.com/efb0a5eccd2caa5135eb54eba6f7f300 \
  --header 'Content-Type: application/json' \
  --data '
{
  "jsonrpc": "2.0",
  "method": "eth_chainId",
  "id": 1
}
'
{
  "jsonrpc": "<string>",
  "id": 123,
  "result": "<string>"
}
Optimism API method eth_chainId retrieves the current chain ID, which is a unique identifier for the blockchain network the node is connected to. The chain ID is crucial for transaction signing to prevent replay attacks across different chains.
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​
Parameters

  • none — This method does not require any parameters.

​
Response

  • result — the current chain ID, encoded as a hexadecimal string. For example, the chain ID for Optimism Mainnet is 0xa.

​
Use case

The eth_chainId method is essential for:
  • Wallets and applications that sign transactions, as the chain ID is used as part of the signing process to ensure transactions are only valid on the intended chain.
  • Applications that interact with multiple blockchain networks and need to confirm the network they are communicating with.

Body

application/json
​
jsonrpc
string
default:2.0
​
method
string
default:eth_chainId
​
id
integer
default:1

Response

200 - application/json

The current chain ID

​
jsonrpc
string
​
id
integer
​
result
string
Last modified on August 7, 2025