# RPC API

MetaMask uses the ethereum.request(args) method to wrap an RPC API.

The API is based on an interface exposed by all Ethereum clients, along with a growing number of methods that may or may not be supported by other wallets.

Tip

All RPC method requests can return errors. Make sure to handle errors for every call to ethereum.request(args).

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# Table of Contents

# Ethereum JSON-RPC Methods

For the Ethereum JSON-RPC API, please see the Ethereum wiki (opens new window).

Important methods from this API include:

# Permissions

MetaMask introduced Web3 Wallet Permissions via EIP-2255 (opens new window). In this permissions system, each RPC method is either restricted or open. If a method is restricted, an external domain (like a web3 site) must have the corresponding permission in order to call it. Open methods, meanwhile, do not require permissions to call, but may require confirmation by the user in order to succeed (e.g. eth_sendTransaction).

Currently, the only permission is eth_accounts, which allows you to access the user's Ethereum address(es). More permissions will be added in the future.

Under the hood, permissions are plain, JSON-compatible objects, with a number of fields that are mostly used internally by MetaMask. The following interface lists the fields that may be of interest to consumers:

interface Web3WalletPermission {
  // The name of the method corresponding to the permission
  parentCapability: string;
  // The date the permission was granted, in UNIX epoch time
  date?: number;
}

The permissions system is implemented in the rpc-cap package (opens new window). If you're interested in learning more about the theory behind this capability-inspired permissions system, we encourage you to take a look at EIP-2255 (opens new window).

# eth_requestAccounts

EIP-1102

This method is specified by EIP-1102 (opens new window). It is equivalent to the deprecated ethereum.enable() provider API method.

Under the hood, it calls wallet_requestPermissions for the eth_accounts permission. Since eth_accounts is currently the only permission, this method is all you need for now.

# Returns

string[] - An array of a single, hexadecimal Ethereum address string.

# Description

Requests that the user provides an Ethereum address to be identified by. Returns a Promise that resolves to an array of a single Ethereum address string. If the user denies the request, the Promise will reject with a 4001 error.

The request causes a MetaMask popup to appear. You should only request the user's accounts in response to user action, such as a button click. You should always disable the button that caused the request to be dispatched, while the request is still pending.

If you can't retrieve the user's account(s), you should encourage the user to initiate an account request.

# Example

document.getElementById('connectButton', connect);
function connect() {
  ethereum
    .request({ method: 'eth_requestAccounts' })
    .then(handleAccountsChanged)
    .catch((error) => {
      if (error.code === 4001) {
        // EIP-1193 userRejectedRequest error
        console.log('Please connect to MetaMask.');
      } else {
        console.error(error);
      }
    });
}

# wallet_getPermissions

Platform Availability

This RPC method is not yet available in MetaMask Mobile.

# Returns

Web3WalletPermission[] - An array of the caller's permissions.

# Description

Gets the caller's current permissions. Returns a Promise that resolves to an array of Web3WalletPermission objects. If the caller has no permissions, the array will be empty.

# wallet_requestPermissions

Platform Availability

This RPC method is not yet available in MetaMask Mobile.

# Parameters

  • Array

    1. RequestedPermissions - The requested permissions.
interface RequestedPermissions {
  [methodName: string]: {}; // an empty object, for future extensibility
}

# Returns

Web3WalletPermission[] - An array of the caller's permissions.

# Description

Requests the given permissions from the user. Returns a Promise that resolves to a non-empty array of Web3WalletPermission objects, corresponding to the caller's current permissions. If the user denies the request, the Promise will reject with a 4001 error.

The request causes a MetaMask popup to appear. You should only request permissions in response to user action, such as a button click.

# Example

document.getElementById('requestPermissionsButton', requestPermissions);
function requestPermissions() {
  ethereum
    .request({
      method: 'wallet_requestPermissions',
      params: [{ eth_accounts: {} }],
    })
    .then((permissions) => {
      const accountsPermission = permissions.find(
        (permission) => permission.parentCapability === 'eth_accounts'
      );
      if (accountsPermission) {
        console.log('eth_accounts permission successfully requested!');
      }
    })
    .catch((error) => {
      if (error.code === 4001) {
        // EIP-1193 userRejectedRequest error
        console.log('Permissions needed to continue.');
      } else {
        console.error(error);
      }
    });
}

# Other RPC Methods

# eth_decrypt

Platform Availability

This RPC method is not yet available in MetaMask Mobile.

# Parameters

  • Array

    1. string - An encrypted message.
    2. string - The address of the Ethereum account that can decrypt the message.

# Returns

string - The decrypted message.

# Description

Requests that MetaMask decrypts the given encrypted message. The message must have been encrypted using the public encryption key of the given Ethereum address. Returns a Promise that resolves to the decrypted message, or rejects if the decryption attempt fails.

See eth_getEncryptionPublicKey for more information.

# Example

ethereum
  .request({
    method: 'eth_decrypt',
    params: [encryptedMessage, accounts[0]],
  })
  .then((decryptedMessage) =>
    console.log('The decrypted message is:', decryptedMessage)
  )
  .catch((error) => console.log(error.message));

# eth_getEncryptionPublicKey

Platform Availability

This RPC method is not yet available in MetaMask Mobile.

# Parameters

  • Array

    1. string - The address of the Ethereum account whose encryption key should be retrieved.

# Returns

string - The public encryption key of the specified Ethereum account.

# Description

Requests that the user shares their public encryption key. Returns a Promise that resolve to the public encryption key, or rejects if the user denied the request.

The public key is computed from entropy associated with the specified user account, using the nacl (opens new window) implementation of the X25519_XSalsa20_Poly1305 algorithm.

# Example

let encryptionPublicKey;
ethereum
  .request({
    method: 'eth_getEncryptionPublicKey',
    params: [accounts[0]], // you must have access to the specified account
  })
  .then((result) => {
    encryptionPublicKey = result;
  })
  .catch((error) => {
    if (error.code === 4001) {
      // EIP-1193 userRejectedRequest error
      console.log("We can't encrypt anything without the key.");
    } else {
      console.error(error);
    }
  });

# Encrypting

The point of the encryption key is of course to encrypt things. Here's an example of how to encrypt a message using eth-sig-util (opens new window):

const ethUtil = require('ethereumjs-util');
const encryptedMessage = ethUtil.bufferToHex(
  Buffer.from(
    JSON.stringify(
      sigUtil.encrypt(
        encryptionPublicKey,
        { data: 'Hello world!' },
        'x25519-xsalsa20-poly1305'
      )
    ),
    'utf8'
  )
);

# wallet_addEthereumChain

EIP-3085

This method is specified by EIP-3085 (opens new window).

# Parameters

  • Array

    1. AddEthereumChainParameter - Metadata about the chain that will be added to MetaMask.

For the rpcUrls and blockExplorerUrls arrays, at least one element is required, and only the first element will be used.

interface AddEthereumChainParameter {
  chainId: string; // A 0x-prefixed hexadecimal string
  chainName: string;
  nativeCurrency: {
    name: string;
    symbol: string; // 2-6 characters long
    decimals: 18;
  };
  rpcUrls: string[];
  blockExplorerUrls?: string[];
  iconUrls?: string[]; // Currently ignored.
}

# Returns

null - The method returns null if the request was successful, and an error otherwise.

# Description

Creates a confirmation asking the user to add the specified chain to MetaMask. The user may choose to switch to the chain once it has been added.

As with any method that causes a confirmation to appear, wallet_addEthereumChain should only be called as a result of direct user action, such as the click of a button.

MetaMask stringently validates the parameters for this method, and will reject the request if any parameter is incorrectly formatted. In addition, MetaMask will automatically reject the request under the following circumstances:

  • If the RPC endpoint doesn't respond to RPC calls.
  • If the RPC endpoint returns a different chain ID when eth_chainId is called.
  • If the chain ID corresponds to any default MetaMask chains.

MetaMask does not yet support chains with native currencies that do not have 18 decimals, but may do so in the future.

# Usage with wallet_switchEthereumChain

We recommend using this method with wallet_addEthereumChain:

try {
  await ethereum.request({
    method: 'wallet_switchEthereumChain',
    params: [{ chainId: '0xf00' }],
  });
} catch (switchError) {
  // This error code indicates that the chain has not been added to MetaMask.
  if (error.code === 4902) {
    try {
      await ethereum.request({
        method: 'wallet_addEthereumChain',
        params: [{ chainId: '0xf00', rpcUrl: 'https://...' /* ... */ }],
      });
    } catch (addError) {
      // handle "add" error
    }
  }
  // handle other "switch" errors
}

# wallet_switchEthereumChain

EIP-3326

This method is specified by EIP-3326 (opens new window).

# Parameters

  • Array

    1. SwitchEthereumChainParameter - Metadata about the chain that MetaMask will switch to.
interface AddEthereumChainParameter {
  chainId: string; // A 0x-prefixed hexadecimal string
}

# Returns

null - The method returns null if the request was successful, and an error otherwise.

If the error code (error.code) is 4902, then the requested chain has not been added by MetaMask, and you have to request to add it via wallet_addEthereumChain.

# Description

Tip

See above for how to use this method with wallet_addEthereumChain.

Creates a confirmation asking the user to switch to the chain with the specified chainId.

As with any method that causes a confirmation to appear, wallet_switchEthereumChain should only be called as a result of direct user action, such as the click of a button.

MetaMask will automatically reject the request under the following circumstances:

  • If the chain ID is malformed
  • If the chain with the specified chain ID has not been added to MetaMask

# wallet_registerOnboarding

Tip

As an API consumer, you are unlikely to have to call this method yourself. Please see the Onboarding Library documentation for more information.

# Returns

boolean - true if the request was successful, false otherwise.

# Description

Registers the requesting site with MetaMask as the initiator of onboarding. Returns a Promise that resolves to true, or rejects if there's an error.

This method is intended to be called after MetaMask has been installed, but before the MetaMask onboarding has completed. You can use this method to inform MetaMask that you were the one that suggested installing MetaMask. This lets MetaMask redirect the user back to your site after onboarding has completed.

Instead of calling this method directly, you should use the @metamask/onboarding library (opens new window).

# wallet_watchAsset

EIP-747

This method is specified by EIP-747 (opens new window).

# Parameters

  • WatchAssetParams - The metadata of the asset to watch.
interface WatchAssetParams {
  type: 'ERC20'; // In the future, other standards will be supported
  options: {
    address: string; // The address of the token contract
    'symbol': string; // A ticker symbol or shorthand, up to 5 characters
    decimals: number; // The number of token decimals
    image: string; // A string url of the token logo
  };
}

# Returns

boolean - true if the the token was added, false otherwise.

# Description

Requests that the user tracks the token in MetaMask. Returns a boolean indicating if the token was successfully added.

Most Ethereum wallets support some set of tokens, usually from a centrally curated registry of tokens. wallet_watchAsset enables web3 application developers to ask their users to track tokens in their wallets, at runtime. Once added, the token is indistinguishable from those added via legacy methods, such as a centralized registry.

# Example

ethereum
  .request({
    method: 'wallet_watchAsset',
    params: {
      type: 'ERC20',
      options: {
        address: '0xb60e8dd61c5d32be8058bb8eb970870f07233155',
        symbol: 'FOO',
        decimals: 18,
        image: 'https://foo.io/token-image.svg',
      },
    },
  })
  .then((success) => {
    if (success) {
      console.log('FOO successfully added to wallet!')
    } else {
      throw new Error('Something went wrong.')
    }
  })
  .catch(console.error)

# Mobile Specific RPC Methods

# wallet_scanQRCode

# Parameters

  • Array

    1. string - (optional) A regular expression for matching arbitrary QR code strings

# Returns

string - The string corresponding to the scanned QR code.

# Description

Requests that the user scans a QR code using their device camera. Returns a Promise that resolves to a string, matching either:

  1. The regex parameter, if provided
  2. An ethereum address, if no regex parameter was provided

If neither condition is met, the Promise will reject with an error.

MetaMask previously introduced this feature per the proposed EIP-945 (opens new window). The functionality was temporarily removed before being reintroduced as this RPC method.

# Example

ethereum
  .request({
    method: 'wallet_scanQRCode',
    // The regex string must be valid input to the RegExp constructor, if provided
    params: ['\\D'],
  })
  .then((result) => {
    console.log(result);
  })
  .catch((error) => {
    console.log(error);
  });