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Builder codes work with the Base-Solana bridge via the hookData mechanism. Currently available for Solana → Base flows only.
1

Get Your Builder Code

When you register on base.dev, you will find a Builder Code under your app’s settings. This is a random string (e.g., k3p9da) that you will use to generate your attribution suffix.
2

Build hookData

ABI-encode the user address, your code, and fee:
bytes memory hookData = abi.encode(
  0xUSER,           // destination address on Base (NOT the Twin)
  0xBUILDER_CODE,   // your builder code in type string memory
  100               // feeBps (100 = 1%)
);
3

Attach to Bridge Message

Set to = BRIDGE_CAMPAIGN_ADDRESS and attach a call to Flywheel.send.
For a bridge with no follow-up call:
to:     <BRIDGE_CAMPAIGN_ADDRESS> // 0xE2AD1C34382410C30d826B019A0B3700F5c4e6c9 on Base Sepolia
amount: 100
call:
  ty:    Call
  to:    <FLYWHEEL_ADDRESS> // 0x00000F14AD09382841DB481403D1775ADeE1179F on Base Sepolia
  value: 0
  data:  abi.encodeWithSelector(
           Flywheel.send.selector,
           <BRIDGE_CAMPAIGN_ADDRESS>, // 0xE2AD1C34382410C30d826B019A0B3700F5c4e6c9 on Base Sepolia
           <wSOL_ADDRESS>,
           hookData
         )
4

Learn More: A Full Implementation Example

Terminally Onchain is a production Next.js app that exposes the bridge via a command terminal UI. Users connect a Solana wallet, type commands such as to bridge and call a contract on Base:You can use Terminally Onchain to test bridge transactions with Builder Codes like so:
bridge 0.0001 sol 0xYOUR_DESTINATION_ADDRESS --with-bc YOUR_BUILDER_CODE --bc-fee YOUR_FEE_BPS
To see how this is implemented, you can take a look at the Github repo:
sol2base/MainContent.tsx
// Constants
const BRIDGE_CAMPAIGN_ADDRESS = "0xE2AD1C34382410C30d826B019A0B3700F5c4e6c9";
const FLYWHEEL_ADDRESS = "0x00000F14AD09382841DB481403D1775ADeE1179F";
const MULTICALL_ADDRESS = "0xcA11bde05977b3631167028862bE2a173976CA11";

// Encode hookData: (address user, string code, uint8 feeBps)
const buildBuilderHookData = (
  destination: string,
  builderCode: string,
  feeBps: number
) => {
  const coder = new AbiCoder();
  return coder.encode(
    ["address", "string", "uint8"],
    [destination, builderCode, feeBps]
  );
};

// Build Flywheel.send call
const buildBuilderCall = (
  destination: string,
  builderCode: string,
  feeBps: number,
  tokenAddress: string
): BaseContractCall => {
  const hookData = buildBuilderHookData(destination, builderCode, feeBps);
  const data = encodeFunctionData({
    abi: FLYWHEEL_ABI,
    functionName: "send",
    args: [BRIDGE_CAMPAIGN_ADDRESS, tokenAddress, hookData],
  });
  return { type: "call", target: FLYWHEEL_ADDRESS, value: "0", data };
};

// Wrap builder + user calls in Multicall (for chained calls)
const buildMulticall = (
  builder: BaseContractCall,
  userCall: BaseContractCall
): BaseContractCall => {
  const data = encodeFunctionData({
    abi: MULTICALL_ABI,
    functionName: "multicall",
    args: [
      [
        { target: builder.target, callData: builder.data },
        { target: userCall.target, callData: userCall.data },
      ],
    ],
  });
  return { type: "delegatecall", target: MULTICALL_ADDRESS, value: "0", data };
};

// Usage: attach builder code to bridge
if (payload.flags.withBc) {
  const builderCall = buildBuilderCall(
    destination,
    builderCode,
    feeBps,
    remoteToken
  );
  callOption = userCall ? buildMulticall(builderCall, userCall) : builderCall;
}

// Set destination to campaign address when using builder codes
const destinationForBridge = builderCode
  ? BRIDGE_CAMPAIGN_ADDRESS
  : payload.destination;

​
Contract Addresses

ContractBase MainnetBase Sepolia
BRIDGE_CAMPAIGN_ADDRESS0x539A97cc4724d5b2740DB98Bc71445448eFC1Bde0xE2AD1C34382410C30d826B019A0B3700F5c4e6c9
FLYWHEEL_ADDRESS0x00000F14AD09382841DB481403D1775ADeE1179F0x00000F14AD09382841DB481403D1775ADeE1179F
MULTICALL_ADDRESS0xcA11bde05977b3631167028862bE2a173976CA110xcA11bde05977b3631167028862bE2a173976CA11