Adding Builder Codes

Integrate Base Builder Codes into an onchain application. Builder Codes append an ERC-8021 attribution suffix to transaction calldata so Base can attribute activity to your app and you can earn referral fees. No smart contract changes required.

When to Use This Skill

Use this skill when a developer asks to:

"Add builder codes to my application"
"How do I append a builder code to my transactions?"
"I want to earn referral fees on Base transactions"
"Integrate builder codes"
Set up transaction attribution on Base

Prerequisites

A Builder Code from base.dev > Settings > Builder Codes
The ox library for generating ERC-8021 suffixes: npm install ox

Integration Workflow

Copy this checklist and track progress:

Builder Codes Integration:
- [ ] Step 1: Detect framework (Required First Step)
- [ ] Step 2: Install dependencies
- [ ] Step 3: Generate the dataSuffix constant
- [ ] Step 4: Apply attribution (framework-specific)
- [ ] Step 5: Verify attribution is working

Framework Detection (Required First Step)

Before implementing, determine the framework in use.

1. Read package.json and scan source files

# Check for framework dependencies
grep -E "wagmi|@privy-io/react-auth|viem|ethers" package.json

# Check for smart wallet / account abstraction usage
grep -rn "useSendCalls\|sendCalls\|ERC-4337\|useSmartWallets" src/

# Check for EOA transaction patterns
grep -rn "useSendTransaction\|sendTransaction\|writeContract\|useWriteContract" src/

# Check Privy version if present
grep "@privy-io/react-auth" package.json

2. Classify into one framework

Framework	Detection Signal
`privy`	`@privy-io/react-auth` in package.json or imports
`wagmi`	`wagmi` in package.json or imports (without Privy)
`viem`	`viem` in package.json, no React framework
`rpc`	`ethers`, `window.ethereum`, or no Web3 library detected

Priority order if multiple are detected: Privy > Wagmi > Viem > Standard RPC

3. Confirm with user

Before proceeding, confirm the detected framework:

"I detected you are using [Framework]. I'll implement builder codes using the [Framework] approach — does that sound right?"

Wait for user confirmation before implementing.

Implementation Path

Privy (@privy-io/react-auth v3.13.0+) → See references/privy.md
Wagmi (without Privy) → See references/wagmi.md
Viem only (no React framework) → See references/viem.md
Standard RPC (ethers.js or raw window.ethereum) → See references/rpc.md

Step 2: Install dependencies

npm install ox

Requires viem >= 2.45.0 for Wagmi/Viem paths. Privy requires @privy-io/react-auth >= 3.13.0.

Step 3: Generate the dataSuffix constant

Create a shared constant (e.g., src/lib/attribution.ts or src/constants/builderCode.ts):

import { Attribution } from "ox/erc8021";

export const DATA_SUFFIX = Attribution.toDataSuffix({
  codes: ["YOUR-BUILDER-CODE"], // Replace with your code from base.dev
});

Step 4: Apply attribution

Follow the framework-specific guide:

Privy Implementation

See references/privy.md — plugin-based, one config change required.

Wagmi Implementation

See references/wagmi.md — add dataSuffix to Wagmi client config.

Viem Implementation

See references/viem.md — add dataSuffix to wallet client.

Standard RPC Implementation

See references/rpc.md — append DATA_SUFFIX to transaction data for ethers.js or raw window.ethereum.

Preferred approach: Configure at the client level so all transactions are automatically attributed. Only use the per-transaction approach if you need conditional attribution.

For Smart Wallets (EIP-5792 sendCalls): See references/smart-wallets.md — pass via capabilities.

Step 5: Verify attribution

base.dev: Check Onchain > Total Transactions for attribution counts
Block explorer: Find tx hash, view input data, confirm last 16 bytes are 8021 repeating
Validation tool: Use builder-code-checker.vercel.app

Key Facts

Builder Codes are ERC-721 NFTs minted on Base
The suffix is appended to calldata; smart contracts ignore it (no upgrades needed)
Gas cost is negligible: 16 gas per non-zero byte
Analytics on base.dev currently support Smart Account (AA) transactions; EOA support is coming (attribution data is preserved)
The dataSuffix plugin in Privy appends to all chains, not just Base. If chain-specific behavior is needed, contact Privy
Privy's dataSuffix plugin is NOT yet supported with @privy-io/wagmi adapter

Finding Transaction Call Sites

When retrofitting an existing project, search for these patterns:

# React hooks (Wagmi)
grep -rn "useSendTransaction\|useSendCalls\|useWriteContract\|useContractWrite" src/

# Viem client calls
grep -rn "sendTransaction\|writeContract\|sendRawTransaction" src/

# Privy embedded wallet calls
grep -rn "sendTransaction\|signTransaction" src/

# ethers.js
grep -rn "signer\.sendTransaction\|contract\.connect" src/

# Raw window.ethereum
grep -rn "window\.ethereum\|eth_sendTransaction" src/

For client-level integration (Wagmi/Viem/Privy), you typically only need to modify the config file — individual transaction call sites remain unchanged.

adding-builder-codes