> ## Documentation Index
> Fetch the complete documentation index at: https://docs.base.org/llms.txt
> Use this file to discover all available pages before exploring further.

# Builder Codes for Agent Developers

> Attribute your AI agent's onchain transactions to your identity on Base and unlock analytics and leaderboard features.

AI agents operate autonomously and send transactions without a user manually triggering each one. Builder Codes give you a way to attribute all of that activity back to your agent's identity on Base.

## Why agents need Builder Codes

* **Attribution** — Every transaction your agent sends is tied to your identity in the Base registry. Without it, your agent's onchain activity is anonymous.
* **Analytics** — Track your agent's transaction volume, user reach, and onchain conversion in [base.dev](https://base.dev).
* **Visibility** — Agents with Builder Codes can appear in discovery surfaces like Base's App Leaderboard and ecosystem spotlights.

## How it works

A Builder Code is a unique identifier (e.g. `bc_a1b2c3d4`) that gets appended to your agent's transaction calldata as an [ERC-8021](https://eip.tools/eip/8021) suffix. Smart contracts ignore the suffix; it is extracted by offchain indexers after the fact. The gas overhead is minimal (16 gas per non-zero byte).

## API reference

### Register your agent

```
POST /v1/agents/builder-codes
```

No authentication required.

| Field           | Type   | Required | Description                               |
| --------------- | ------ | -------- | ----------------------------------------- |
| `walletAddress` | string | Yes      | Your agent's EVM wallet address (`0x...`) |

Returns the builder code for the given wallet. The same wallet address always returns the same code.

```bash Terminal theme={null}
curl -X POST https://api.base.dev/v1/agents/builder-codes \
  -H "Content-Type: application/json" \
  -d '{
    "walletAddress": "<your-wallet-address>"
  }'
```

```json Response theme={null}
{
  "builderCode": "bc_a1b2c3d4",
  "walletAddress": "0x..."
}
```

<Info>
  Already registered? Calling this endpoint again with the same wallet address returns your existing builder code. Safe to call on every deploy.
</Info>

## Using the Base skill

If you're using an AI coding tool (Claude Code, Cursor, Codex), install the Base skills package and let the skill handle registration end-to-end:

```bash Terminal theme={null}
npx skills add base/skills
```

Then ask your agent: **"Register my agent for a builder code on Base.dev."**

The skill handles wallet validation, calls the registration API, writes the returned code to `src/constants/builderCode.ts`, installs `ox`, and wires the ERC-8021 `dataSuffix` into your transaction client (viem, ethers.js, or managed service).

## Verify attribution

To confirm your Builder Code is being appended correctly:

**1. Check base.dev**

* Visit [base.dev](https://base.dev)
* Select **Onchain** from the transaction type dropdown
* Under the Total Transactions section, attribution counts increment when transactions with your code are processed

**2. Use a block explorer (Basescan, Etherscan, etc.)**

* Find your transaction hash
* View the input data field
* Verify the last 16 bytes are the `8021` repeating
* Decode the suffix to confirm your Builder Code is present

**3. Open source tools**

* Use the [Builder Code Validation](https://builder-code-checker.vercel.app/) tool
* Select transaction type
* Enter the transaction or UserOperation hash
* Click the **Check Attribution** button

## Next steps

<CardGroup cols={2}>
  <Card title="Builder Codes overview" icon="book-open" href="/apps/builder-codes/builder-codes">
    Learn how Builder Codes work across apps, wallets, and agents.
  </Card>
</CardGroup>