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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.

note

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

Try Ethereum methods

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Ethereum JSON-RPC methods​

For the Ethereum JSON-RPC API, please see the Ethereum wiki.

Important methods from this API include:

Restricted methods​

MetaMask introduced Web3 Wallet Permissions via EIP-2255. In this permissions system, each RPC method is either restricted or unrestricted. If a method is restricted, the caller must have the corresponding permission in order to call it. Unrestricted methods, meanwhile, have no corresponding permission. Some of them still rely upon permissions to succeed though (for example, the signing methods require that you have the eth_accounts permission for the signer account), and some require confirmation by the user (for example, wallet_addEthereumChain).

With the exception of MetaMask Flask, the only existing 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;
}

If you're interested in learning more about the theory behind this capability-inspired permissions system, see EIP-2255.

eth_requestAccounts​

EIP-1102

This method is specified by EIP-1102. It's 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 is 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 rejects 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);
      }
    });
}

Unrestricted methods​

wallet_addEthereumChain​

EIP-3085

This method is specified by EIP-3085.

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 rejects the request if any parameter is incorrectly formatted. In addition, MetaMask automatically rejects the request under the following circumstances:

  • If the RPC endpoint doesn't respond to RPC calls.
    note

    Calls are made from the extension's background page, not the foreground page. If you use an origin allowlist, they're blocked.

  • 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.

Use 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 (switchError.code === 4902) {
    try {
      await ethereum.request({
        method: 'wallet_addEthereumChain',
        params: [
          {
            chainId: '0xf00',
            chainName: '...',
            rpcUrls: ['https://...'] /* ... */,
          },
        ],
      });
    } catch (addError) {
      // handle "add" error
    }
  }
  // handle other "switch" errors
}

wallet_switchEthereumChain​

EIP-3326

This method is specified by EIP-3326.

Parameters​

  • Array

    1. SwitchEthereumChainParameter - Metadata about the chain that MetaMask will switch to.
interface SwitchEthereumChainParameter {
  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 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 automatically rejects the request:

  • 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're unlikely to have to call this method yourself. See the how to use the onboarding library 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.

wallet_watchAsset​

EIP-747

This method is specified by EIP-747.

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 11 characters
    decimals: number; // The number of token decimals
    image: string; // A string url of the token logo
  };
}

Returns​

boolean - true if 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 RPC methods​

The following methods are specific to MetaMask Mobile.

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 rejects with an error.

MetaMask previously introduced this feature per the proposed EIP-945. 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);
  });