EIPs/EIPS/eip-695.md

---
eip: 695
title: Create `eth_chainId` method for JSON-RPC
author: Isaac Ardis <isaac.ardis@gmail.com>, Wei Tang (@sorpaas), Fan Torchz (@tcz001), Erik Marks (@rekmarks)
discussions-to: https://ethereum-magicians.org/t/eip-695-create-eth-chainid-method-for-json-rpc/1845
type: Standards Track
category: Interface
status: Final
created: 2017-08-21
requires: 155
---

## Simple Summary

Include `eth_chainId` method in `eth_`-namespaced JSON-RPC methods.

## Abstract

The `eth_chainId` method should return a single STRING result
for an integer value in hexadecimal format, describing the
currently configured `CHAIN_ID` value used for signing replay-protected transactions,
introduced by [EIP-155](./eip-155.md).

## Motivation

Currently although we can use `net_version` RPC call to get the
current network ID, there's no RPC for querying the chain ID. This
makes it impossible to determine the current actual blockchain using
the RPC.

## Specification

### `eth_chainId`

Returns the currently configured chain ID, a value used in replay-protected transaction
signing as introduced by [EIP-155](./eip-155.md).

The chain ID returned should always correspond to the information in the current known
head block. This ensures that caller of this RPC method can always use the retrieved
information to sign transactions built on top of the head.

If the current known head block does not specify a chain ID, the client should treat any
calls to `eth_chainId` as though the method were not supported, and return a suitable
error.

#### Parameters

None.

#### Returns

`QUANTITY` - integer of the current chain ID.

#### Example

```js
curl -X POST --data '{"jsonrpc":"2.0","method":"eth_chainId","params":[],"id":83}'

// Result
{
  "id": 83,
  "jsonrpc": "2.0",
  "result": "0x3d" // 61
}
```

## Rationale

An ETH/ETC client can accidentally connect to an ETC/ETH RPC
endpoint without knowing it unless it tries to sign a transaction or
it fetch a transaction that is known to have signed with a chain
ID. This has since caused trouble for application developers, such as
MetaMask, to add multi-chain support.

## Backwards Compatibility

Not relevant.

## Security Considerations

Consumers should prefer `eth_chainId` over `net_version`, so that they can reliably identify chain they are communicating with.

Implementers should take care to implement `eth_chainId` correctly and promote its use, since the chain ID is critical in replay attack prevention as described in [EIP-155](./eip-155.md), and consumers will rely on it to identify the chain they are communicating with.

## Implementation

- [Parity PR](https://github.com/paritytech/parity/pull/6329)
- [Geth PR](https://github.com/ethereum/go-ethereum/pull/17617)
- [Geth Classic PR](https://github.com/ethereumproject/go-ethereum/pull/336)

## Reference

Return value `QUANTITY` adheres to standard JSON RPC hex value encoding, as documented in the [Ethereum Wiki](https://github.com/ethereum/wiki/wiki/JSON-RPC#hex-value-encoding).

## Copyright

Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).