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Sign a typed-data message

EIP-712 typed data is the standard for signatures a contract will verify later — permits, orders, votes. Unlike a raw message, Core renders every field on the approval screen, so the user sees amount: 1000 and deadline: …, not a hash.

This guide signs an ERC-20 permit (EIP-2612) — the most common typed-data message in production.

1. Build the typed payload​

const domain = {
  name: 'USD Coin',            // must match the token contract
  version: '2',
  chainId: 43114,
  verifyingContract: '0xB97EF9Ef8734C71904D8002F8b6Bc66Dd9c48a6E', // USDC
};

const types = {
  Permit: [
    { name: 'owner', type: 'address' },
    { name: 'spender', type: 'address' },
    { name: 'value', type: 'uint256' },
    { name: 'nonce', type: 'uint256' },
    { name: 'deadline', type: 'uint256' },
  ],
};

const message = {
  owner: account,
  spender: spenderAddress,
  value: '1000000',                                  // 1 USDC (6 decimals)
  nonce: await usdc.read.nonces([account]),          // from the token
  deadline: Math.floor(Date.now() / 1000) + 3600,    // 1 hour
};

The domain binds the signature to one contract on one chain; the nonce makes it single-use. Get the nonce from the token contract itself.

2. Request the signature​

const signature = await provider.request({
  method: 'eth_signTypedData_v4',
  params: [
    account,
    JSON.stringify({
      domain,
      message,
      primaryType: 'Permit',
      types: {
        EIP712Domain: [
          { name: 'name', type: 'string' },
          { name: 'version', type: 'string' },
          { name: 'chainId', type: 'uint256' },
          { name: 'verifyingContract', type: 'address' },
        ],
        ...types,
      },
    }),
  ],
});

Note the shape: params are [address, jsonString], and the JSON must include EIP712Domain in types even though the provider hashes it for you.

3. Use the signature​

Split it and call the contract:

const r = signature.slice(0, 66);
const s = '0x' + signature.slice(66, 130);
const v = parseInt(signature.slice(130, 132), 16);

await usdc.write.permit([account, spenderAddress, value, deadline, v, r, s]);

The spender can now transferFrom up to value until deadline — one signature instead of an approve transaction.

Handle the decline​

A 4001 rejection means the user said no on the approval screen. Treat it as a cancelled action, not a failure — see error codes.