Build a Paying Agent

Give your AI agent a wallet. Let it fetch paid web content automatically using the x402 protocol — no gas, no on-chain transactions per request.

Quickstart

1. 1. Install the SDK

   npm install @circle-fin/x402-batching @x402/evm

   Import GatewayClient from @circle-fin/x402-batching/client — not the root package.

2. 2. Set environment variables

   # .env.local
   NANOCRAWL_BUYER_PRIVATE_KEY=0x<your-wallet-private-key>
   NANOCRAWL_BUYER_WALLET=0x<your-wallet-address>

3. 3. Fund the Gateway balance (once)

   import { GatewayClient } from '@circle-fin/x402-batching/client'
   
   const client = new GatewayClient({
     chain: 'arcTestnet',
     privateKey: process.env.NANOCRAWL_BUYER_PRIVATE_KEY,
   })
   
   // One-time: move on-chain USDC into the Gateway
   await client.deposit('1')  // deposit 1 USDC

   The Gateway balance is what gets debited on each client.pay() call. On-chain USDC is not spent per request.

4. 4. Fetch paid content

   // Handles the full x402 round-trip automatically:
   //   GET → 402 → sign EIP-3009 off-chain → retry with PAYMENT-SIGNATURE
   const result = await client.pay('https://nanocrawl.vercel.app/products/1')
   
   console.log(result.response)  // the paid content (JSON)
   console.log(result.transaction)  // Circle settlement UUID

MCP Server Integration

To give Claude or any MCP-compatible agent a paying wallet, wrap client.pay() as an MCP tool:

server.tool('fetch_paid_page', {
  url: z.string().url(),
  budget: z.number().optional(),
}, async ({ url }) => {
  const result = await client.pay(url)
  return { content: [{ type: 'text', text: JSON.stringify(result.response) }] }
})

The agent sees a normal tool call. Payment happens transparently.

How Payment Works

Test Against NanoCrawl

Need test USDC? Get it from faucet.circle.com, then call client.deposit().

Private Payments via Unlink

By default, your agent's wallet address is visible on-chain as a Gateway participant. For agents where data-source privacy matters — trading bots, research agents — you can shield your identity using Unlink, a ZK privacy pool on Base Sepolia.

// Use Base Sepolia for the Unlink flow (Unlink is deployed here, not Arc)
const burner = await BurnerWallet.create()
await burner.fundFromPool(unlinkClient, { token: USDC, amount: '5000000' })

const gateway = new GatewayClient({
  chain: 'baseSepolia',            // ← Base Sepolia, not arcTestnet
  privateKey: burner.privateKey,
})
await gateway.deposit('5.00')

// Crawl loop — identical to the standard flow
for (const url of urls) {
  await gateway.pay(url)
}

// Session end — return funds, dispose burner
await gateway.withdraw(remaining)
await burner.depositToPool(unlinkClient, { ... })
burner.deleteKey()

NanoCrawl accepts payments on both Arc Testnet and Base Sepolia. No seller-side changes needed — the 402 response advertises both networks.