Builder Codes for Wallet Developers

Implement the dataSuffix capability in your wallet to enable Builder Code attribution.

Overview

Wallet providers need to support the dataSuffix capability to enable attribution. This involves accepting the capability and appending the suffix to the calldata before signing.

1. Support the dataSuffix Capability

   Your wallet should accept a dataSuffix object in the capabilities object 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 or User Operation, 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

   Append to userOp.callData (not the transaction-level calldata).

   // Minimal example for ERC-4337
   function applySuffixToUserOp(userOp, capabilities) {
     const suffix = capabilities.dataSuffix?.value
     if (!suffix) return userOp
   
     return {
       ...userOp,
       // Append suffix bytes to the UserOp callData
       callData: userOp.callData + suffix.slice(2)
     }
   }
   
3. Add Wallet Attribution (Optional)

   Wallets may also include their own attribution code (their own ERC-8021 suffix) by prepending the wallet’s suffix before the app’s.

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

   Example:

   finalSuffix = walletSuffix + appSuffix
   

   This ensures both the app and the wallet receive onchain attribution.