Builder Codes for Wallet Providers#

If you are building a wallet and want to support ERC-8021 attribution for apps running on X Layer, implement the following.

Implementation#

1. Support the dataSuffix Capability#

Your wallet should accept a dataSuffix object in the capabilities field of wallet_sendCalls.

type DataSuffixCapability = {
  value: `0x${string}`;  // hex-encoded bytes provided by the app
  optional?: boolean;    // whether the capability is optional
}

2. Append Suffix to Calldata#

When constructing the transaction, extract the dataSuffix and append it to the calldata.

EOA Transactions — append to tx.data:

// Minimal example for EOA
function applySuffixToEOA(tx, capabilities) {
  const suffix = capabilities.dataSuffix?.value
  if (!suffix) return tx

  return {
    ...tx,
    // Append suffix bytes (remove 0x prefix from suffix if tx.data has it)
    data: tx.data + suffix.slice(2)
  }
}

ERC-4337 User Operations — not supported yet.

3. Add Wallet Attribution (Optional)#

Wallets may include their own Builder Code by prepending the wallet's suffix before the app's suffix.

• No interaction required with apps: The wallet handles this independently.
• Multi-code support: ERC-8021 natively supports multiple attribution codes.

finalSuffix = walletSuffix + appSuffix

This ensures both the app and the wallet receive onchain attribution on X Layer.

Get your Builder Code: Go to the OKX developer portal, verify your address, then create your Builder Code on the Builder Code page.