EIPs/EIPS/eip-3085.md

---
eip: 3085
title: Wallet Add Ethereum Chain RPC Method (`wallet_addEthereumChain`)
author: Erik Marks (@rekmarks), Pedro Gomes (@pedrouid)
discussions-to: https://ethereum-magicians.org/t/eip-3085-wallet-addethereumchain/5469
status: Review
type: Standards Track
category: Interface
created: 2020-11-01
requires: 155, 695
---

## Simple Summary

An RPC method for adding Ethereum chains to wallet applications.

## Abstract

The `wallet_addEthereumChain` RPC method allows Ethereum applications ("dapps") to suggest chains to be added to the user's wallet application.
The caller must specify a chain ID and some chain metadata.
The wallet application may arbitrarily refuse or accept the request.
`null` is returned if the chain was added, and an error otherwise.

## Motivation

All dapps require the user to interact with one or more Ethereum chains in order to function.
Any given chain may or may not be supported by the user's wallet application.
`wallet_addEthereumChain` enables dapps to request chains to be added to the user's wallet.
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](https://www.ietf.org/rfc/rfc2119.txt).

### `wallet_addEthereumChain`

The method accepts a single object parameter, with a `chainId` and some chain metadata.
The method returns `null` if the chain was added to the wallet, and an error otherwise.

The wallet **MAY** reject the request for any reason.

> Note that this method makes **no** statement about whether the wallet should change the user's currently selected chain, if the wallet has a concept thereof.

#### Parameters

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

```typescript
interface AddEthereumChainParameter {
  chainId: string;
  blockExplorerUrls?: string[];
  chainName?: string;
  iconUrls?: string[];
  nativeCurrency?: {
    name: string;
    symbol: string;
    decimals: number;
  };
  rpcUrls?: string[];
}
```

Only the `chainId` is required per this specification, but a wallet **MAY** require any other fields listed, impose additional requirements on them, or ignore them outright.
If a field does not meet the requirements of this specification and the wallet does not ignore the field, the wallet **MUST** reject the request.

- `chainId`
  - **MUST** specify the integer ID of the chain as a hexadecimal string, per the [`eth_chainId`](./eip-695.md) Ethereum RPC method.
  - The wallet **SHOULD** compare the specified `chainId` value with the `eth_chainId` return value from the endpoint.
    If these values are not identical, the wallet **MUST** reject the request.
- `blockExplorerUrls`
  - If provided, **MUST** specify one or more URLs pointing to block explorer web sites for the chain.
- `chainName`
  - If provided, **MUST** specify a human-readable name for the chain.
- `iconUrls`
  - If provided, **MUST** specify one or more URLs pointing to reasonably sized images that can be used to visually identify the chain.
- `nativeCurrency`
  - If provided, **MUST** describe the native currency of the chain using the `name`, `symbol`, and `decimals` fields.
    - `decimals` **MUST** be a non-negative integer.
    - `name` and `symbol` **SHOULD** be human-readable strings.
- `rpcUrls`
  - If provided, **MUST** specify one or more URLs pointing to RPC endpoints that can be used to communicate with the chain.

All URL strings **MUST** include the protocol component of the URL.
HTTPS **SHOULD** always be used over HTTP.

#### Returns

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

A request to add a chain that was already added **SHOULD** be considered successful.

The wallet **MUST NOT** allow the same `chainId` to be added multiple times.
See [Security Considerations](#security-considerations) for more information.

### Examples

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

To add the Goerli test chain:

```json
{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "wallet_addEthereumChain",
  "params": [
    {
      "chainId": "0x5",
      "chainName": "Goerli",
      "rpcUrls": ["https://goerli.infura.io/v3/INSERT_API_KEY_HERE"],
      "nativeCurrency": {
        "name": "Goerli ETH",
        "symbol": "gorETH",
        "decimals": 18
      },
      "blockExplorerUrls": ["https://goerli.etherscan.io"]
    }
  ]
}
```

To add POA Network's xDAI chain:

```json
{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "wallet_addEthereumChain",
  "params": [
    {
      "chainId": "0x64",
      "chainName": "xDAI Chain",
      "rpcUrls": ["https://dai.poa.network"],
      "iconUrls": [
        "https://xdaichain.com/fake/example/url/xdai.svg",
        "https://xdaichain.com/fake/example/url/xdai.png"
      ],
      "nativeCurrency": {
        "name": "xDAI",
        "symbol": "xDAI",
        "decimals": 18
      }
    }
  ]
}
```

In the above example, notice that the `iconUrls` array contains URLs pointing to two different image formats.

A success response:

```json
{
  "id": 1,
  "jsonrpc": "2.0",
  "result": null
}
```

A failure response:

```json
{
  "id": 1,
  "jsonrpc": "2.0",
  "error": {
    "code": 4001,
    "message": "The user rejected the request."
  }
}
```

## Rationale

The design of `wallet_addEthereumChain` is deliberately ignorant of what it means to "add" a chain to a wallet.
The meaning of "adding" a chain to a wallet depends on the wallet implementation.

When calling the method, specifying the `chainId` will always be necessary, since in the universe of Ethereum chains, the [EIP-155](./eip-155.md) chain ID is effectively the chain GUID.
The remaining parameters amount to what, in the estimation of the authors, a wallet will minimally require in order to effectively support a chain and represent it to the user.
The network ID (per the `net_version` RPC method) is omitted since it is effectively superseded by the chain ID.

For [security reasons](#security-considerations), a wallet should always attempt to validate the chain metadata provided by the requester, and may choose to fetch the metadata elsewhere entirely.
Either way, only the wallet can know which chain metadata it needs from the requester in order to "add" the chain.
Therefore, all parameters except `chainId` are specified as optional, even though a wallet may require them in practice.

This specification does not mandate that the wallet "switches" its "active" or "currently selected" chain after a successful request, if the wallet has a concept thereof.
Just like the meaning of "adding" a chain, "switching" between chains is a wallet implementation detail, and therefore out of scope.

For related work, see [EIP-2015](./eip-2015.md).

## Security Considerations

`wallet_addEthereumChain` is a powerful method that exposes the end user to serious risks if implemented incorrectly.
Many of these risks can be avoided by validating the request data in the wallet, and clearly disambiguating different chains in the wallet UI.

### Chain IDs

Since the chain ID used for transaction signing determines which chain the transaction is valid for, handling the chain ID correctly is of utmost importance.
The wallet should:

- Ensure that a submitted chain ID is valid.
  - It should be a `0x`-prefixed hexadecimal string per [EIP-695](./eip-695.md), and parse to an integer number.
- Prevent the same chain ID from being added multiple times.
  - See the next section for how to handle multiple RPC endpoints.
- Only use the submitted chain ID to sign transactions, **never** a chain ID received from an RPC endpoint.
  - A malicious or faulty endpoint could return arbitrary chain IDs, and potentially cause the user to sign transactions for unintended chains.
- Verify that the specified chain ID matches the return value of `eth_chainId` from the endpoint, as described [above](#parameters).

### RPC Endpoints and RPC URLs

Wallets generally interact with chains via an RPC endpoint, identified by some URL.
Most wallets ship with a set of chains and corresponding trusted RPC endpoints.
The endpoints identified by the `rpcUrls` parameter cannot be assumed to be honest, correct, or even pointing to the same chain.
Moreover, even trusted endpoints can expose users to privacy risks depending on their data collection practices.

Therefore, the wallet should:

- Inform users that their on-chain activity and IP address will be exposed to RPC endpoints.
- If an endpoint is unknown to the wallet, inform users that the endpoint may behave in unexpected ways.
- Observe good web security practices when interacting with the endpoint, such as require HTTPS.
- Clearly inform the user which RPC URL is being used to communicate with a chain at any given moment, and inform the user of the risks of using multiple RPC endpoints to interact with the same chain.

### Validating Chain Data

A wallet that implements `wallet_addEthereumChain` should expect to encounter requests for chains completely unknown to the wallet maintainers.
That said, community resources exist that can be leveraged to verify requests for many Ethereum chains.
The wallet should maintain a list of known chains, and verify requests to add chains against that list.
Indeed, a wallet may even prefer its own chain metadata over anything submitted with a `wallet_addEthereumChain` request.

### UX

Adding a new chain to the wallet can have significant implications for the wallet's functionality and the experience of the user.
A chain should never be added without the explicit consent of the user, and different chains should be clearly differentiated in the wallet UI.
In service of these goals, the wallet should:

- When receiving a `wallet_addEthereumChain` request, display a confirmation informing the user that a specific requester has requested that the chain be added.
- Ensure that any chain metadata, such as `nativeCurrency` and `blockExplorerUrls`, are validated and used to maximum effect in the UI.
- If any images are provided via `iconUrls`, ensure that the user understands that the icons could misrepresent the actual chain added.
- If the wallet UI has a concept of a "currently selected" or "currently active" chain, ensure that the user understands when a chain added using `wallet_addEthereumChain` becomes selected.

### Preserving User Privacy

Although a request to add a chain that was already added should generally be considered a success, treating such requests as _automatic_ successes leaks information to requesters about the chains a user has added to their wallet.
In the interest of preserving user privacy, implementers of `wallet_addEthereumChain` should consider displaying user confirmations even in these cases.
If the user denies the request, the wallet should return the same user rejection error as normal so that requesters cannot learn which chains are supported by the wallet without explicit permission to do so.

## Copyright

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