Skill

sign-evm-message

Name: sign-evm-message
Author: MetaMask

sign EVM messages with MetaMask

Published by MetaMask Updated Jul 13

Covers Auth Web3 Ethereum

Description

Sign messages with MetaMask using personal_sign and eth_signTypedData_v4 via the EIP-1193 provider, plus the connectAndSign shortcut

SKILL.md

Sign EVM Messages with MetaMask Connect

When to use

Use this skill when:

Signing a plaintext message with personal_sign for authentication or verification
Signing structured EIP-712 typed data with eth_signTypedData_v4 for permits, orders, or typed messages
Using the connectAndSign shortcut to connect and sign in a single user approval
Handling signature errors and user rejections

Workflow

Step 1: Get the provider and connected account

Ensure the client is connected before requesting a signature:

import { createEVMClient, getInfuraRpcUrls } from '@metamask/connect-evm';

const client = await createEVMClient({
  dapp: { name: 'My DApp', url: window.location.href },
  api: {
    supportedNetworks: {
      ...getInfuraRpcUrls({ infuraApiKey: 'YOUR_INFURA_KEY', chainIds: ['0x1'] }),
    },
  },
});

const { accounts } = await client.connect({ chainIds: ['0x1'] });
const provider = client.getProvider();
const account = accounts[0]; // Address (0x-prefixed hex)

Step 2: Sign with personal_sign

personal_sign signs a UTF-8 message. The params order is [message, account] where message is a hex-encoded string:

// Convert message to hex
const message = 'Hello, MetaMask!';
const hexMessage = '0x' + Array.from(new TextEncoder().encode(message))
  .map((b) => b.toString(16).padStart(2, '0'))
  .join('');

try {
  const signature = await provider.request({
    method: 'personal_sign',
    params: [hexMessage, account],
  });

  console.log('Signature:', signature);
  // signature is a Hex string: 0x...
} catch (err: any) {
  if (err.code === 4001) {
    console.log('User rejected the signature request');
    return;
  }
  throw err;
}

MetaMask also accepts a raw UTF-8 string for the message parameter, but hex encoding is the canonical format per EIP-191.

Step 3: Sign EIP-712 typed data with eth_signTypedData_v4

Build the full EIP-712 typed data structure with types, primaryType, domain, and message, then pass it as a JSON string:

const typedData = {
  types: {
    EIP712Domain: [
      { name: 'name', type: 'string' },
      { name: 'version', type: 'string' },
      { name: 'chainId', type: 'uint256' },
      { name: 'verifyingContract', type: 'address' },
    ],
    Mail: [
      { name: 'from', type: 'Person' },
      { name: 'to', type: 'Person' },
      { name: 'contents', type: 'string' },
    ],
    Person: [
      { name: 'name', type: 'string' },
      { name: 'wallet', type: 'address' },
    ],
  },
  primaryType: 'Mail',
  domain: {
    name: 'Ether Mail',
    version: '1',
    chainId: 1,
    verifyingContract: '0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC',
  },
  message: {
    from: { name: 'Alice', wallet: '0xAliceAddress' },
    to: { name: 'Bob', wallet: '0xBobAddress' },
    contents: 'Hello Bob!',
  },
};

try {
  const signature = await provider.request({
    method: 'eth_signTypedData_v4',
    params: [account, JSON.stringify(typedData)],
  });

  console.log('Typed data signature:', signature);
} catch (err: any) {
  if (err.code === 4001) {
    console.log('User rejected the typed data signature');
    return;
  }
  throw err;
}

Step 4: ERC-20 Permit (EIP-2612) example

A common use case for eth_signTypedData_v4 is signing ERC-20 permit approvals:

const permitData = {
  types: {
    EIP712Domain: [
      { name: 'name', type: 'string' },
      { name: 'version', type: 'string' },
      { name: 'chainId', type: 'uint256' },
      { name: 'verifyingContract', type: 'address' },
    ],
    Permit: [
      { name: 'owner', type: 'address' },
      { name: 'spender', type: 'address' },
      { name: 'value', type: 'uint256' },
      { name: 'nonce', type: 'uint256' },
      { name: 'deadline', type: 'uint256' },
    ],
  },
  primaryType: 'Permit',
  domain: {
    name: 'USD Coin',
    version: '2',
    chainId: 1,
    verifyingContract: '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48', // USDC
  },
  message: {
    owner: account,
    spender: '0xSpenderContractAddress',
    value: '1000000', // 1 USDC (6 decimals)
    nonce: 0,
    deadline: Math.floor(Date.now() / 1000) + 3600, // 1 hour
  },
};

const signature = await provider.request({
  method: 'eth_signTypedData_v4',
  params: [account, JSON.stringify(permitData)],
});

Step 5: Use connectAndSign for single-approval flow

connectAndSign connects and signs a personal_sign message in one user interaction:

// For authentication, never sign a static string — it is replayable.
// Use an EIP-4361 (SIWE) formatted message with a server-issued nonce:
const siweMessage = [
  `${window.location.host} wants you to sign in with your Ethereum account:`,
  '', // account is filled by your SIWE library or template
  'Sign in to My DApp',
  '',
  `URI: ${window.location.origin}`,
  'Version: 1',
  `Chain ID: 1`,
  `Nonce: ${serverIssuedNonce}`, // fetched from your backend
  `Issued At: ${new Date().toISOString()}`,
].join('\n');

const { accounts, chainId, signature } = await client.connectAndSign({
  message: siweMessage,
  chainIds: ['0x1'],
});

console.log('Connected account:', accounts[0]);
console.log('Signature:', signature);

This is ideal for sign-in-with-Ethereum (SIWE) flows where you want the user to connect and prove ownership in a single step — verify the signature, nonce, and domain server-side.

Step 6: Handle errors

try {
  const signature = await provider.request({
    method: 'personal_sign',
    params: [hexMessage, account],
  });
} catch (err: any) {
  switch (err.code) {
    case 4001:
      // User rejected — show a message, offer retry
      break;
    case -32002:
      // Request pending — another signing request is in progress
      break;
    default:
      // Unexpected error
      console.error('Signing failed:', err);
  }
}

Important Notes

personal_sign params order is [message, account] — not [account, message]. Getting this wrong will produce an invalid signature or an error.
eth_signTypedData_v4 params are [account, typedDataJSON] — the typed data must be passed as a JSON.stringify'd string, not as a raw object.
The EIP712Domain type must be declared in types even though primaryType is never EIP712Domain. It defines the domain separator fields.
connectAndSign only supports personal_sign — for typed data signing during connection, use connectWith with method: 'eth_signTypedData_v4' instead.
Chain IDs in typed data domain.chainId are integers (e.g., 1), while chain IDs in SDK calls are hex strings (e.g., '0x1'). Don't mix them up.
Error code 4001 is a deliberate user rejection — handle gracefully with a retry option.
Error code -32002 means a request is pending — do not fire another sign request until the user responds.
Always connect before signing — personal_sign and eth_signTypedData_v4 require an active account. Call client.connect() first or use connectAndSign.

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