EIP3326 - Wallet Switch Ethereum Chain RPC Method (`wallet_switchEthereumChain`)

# Simple Summary

An RPC method for switching the wallet's active Ethereum chain.

# Abstract

The wallet_switchEthereumChain RPC method allows Ethereum applications ("dapps") to request that the wallet switches its active Ethereum chain, if the wallet has a concept thereof. The caller must specify a chain ID. The wallet application may arbitrarily refuse or accept the request. null is returned if the active chain was switched, and an error otherwise.

Important cautions for implementers of this method are included in the Security Considerations section.

# Motivation

All dapps require the user to interact with one or more Ethereum chains in order to function. Some wallets only supports interacting with one chain at a time. We call this the wallet's "active chain". wallet_switchEthereumChain enables dapps to request that the wallet switches its active chain to whichever one is required by the dapp. This enables UX improvements for both dapps and wallets.

# Specification

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 (opens new window).

# `wallet_switchEthereumChain`

The method accepts a single object parameter with a chainId field. The method returns null if the wallet switched its active chain, and an error otherwise.

The method presupposes that the wallet has a concept of a single "active chain". The active chain is defined as the chain that the wallet is forwarding RPC requests to.

# Parameters

wallet_switchEthereumChain accepts a single object parameter, specified by the following TypeScript interface:

interface SwitchEthereumChainParameter {
  chainId: string;
}

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If a field does not meet the requirements of this specification, the wallet MUST reject the request.

chainId
- MUST specify the integer ID of the chain as a hexadecimal string, per the eth_chainId Ethereum RPC method.
- The chain ID MUST be known to the wallet.
- The wallet MUST be able to switch to the specified chain and service RPC requests to it.

# Returns

The method MUST return null if the request was successful, and an error otherwise.

If the wallet does not have a concept of an active chain, the wallet MUST reject the request.

# Examples

These examples use JSON-RPC, but the method could be implemented using other RPC protocols.

To switch to Mainnet:

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "wallet_switchEthereumChain",
  "params": [
    {
      "chainId": "0x1",
    }
  ]
}

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To switch to the Goerli test chain:

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "wallet_switchEthereumChain",
  "params": [
    {
      "chainId": "0x5",
    }
  ]
}

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# Rationale

The purpose wallet_switchEthereumChain is to provide dapps with a way of requesting to switch the wallet's active chain, which they would otherwise have to ask the user to do manually.

The method accepts a single object parameter to allow for future extensibility at virtually no cost to implementers and consumers.

For related work, see EIP-3085: wallet_addEthereumChain and EIP-2015: wallet_updateEthereumChain. wallet_switchEthereumChain intentionally forgoes the chain metadata parameters included in those EIPs, since it is purely concerned with switching the active chain, regardless of RPC endpoints or any other metadata associated therewith.

# Security Considerations

For wallets with a concept of an active chain, switching the active chain has significant implications for pending RPC requests and the user's experience. If the active chain switches without the user's awareness, a dapp could induce the user to take actions for unintended chains.

In light of this, the wallet should:

Display a confirmation whenever a wallet_switchEthereumChain is received, clearly identifying the requester and the chain that will be switched to.
- The confirmation used in EIP-1102 may serve as a point of reference.
When switching the active chain, cancel all pending RPC requests and chain-specific user confirmations.

# Preserving User Privacy

Automatically rejecting requests for chains that aren't supported or have yet to be added by the wallet allows requesters to infer which chains are supported by the wallet. Wallet implementers should consider whether this communication channel violates any security properties of the wallet, and if so, take appropriate steps to mitigate it.