x402 Micropayments: How AI Agents Pay for Data on Base L2

HTTP 402 — "Payment Required" — has been reserved since 1996. x402 finally makes it real. Here's how autonomous agents are using the protocol to pay for data in real-time, using Support Local Businesses' live payment rail as the working example.

What is x402?

x402 is an open standard for machine-to-machine HTTP payments. When a server returns a 402 Payment Required response, it includes a payment payload in the X-Payment-Required header. The client resolves the payment on Base L2 and retries with a X-Payment-Payload header containing the signed transaction.

No API keys. No subscription sign-ups. No billing portals. The agent pays exactly for what it consumes, in USDC, on Base.

How the Payment Flow Works

The full handshake in four steps:

# Step 1 — Agent makes a request (first 100 free)
GET /api/v1/businesses?zip=33601&category=plumber HTTP/1.1
Host: support-local-businesses.com
X-Agent-Id: my-research-agent/1.0

Step 2 — After free tier, server returns 402
HTTP/1.1 402 Payment Required
Content-Type: application/json
X-Payment-Required: {
  "version": "1.0",
  "scheme": "exact",
  "network": "base",
  "chainId": 8453,
  "maxAmountRequired": "1000",
  "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  "payTo": "0x0cF67aB1D0C843F67bC64D507A5627a41AE5BBC0",
  "memo": "slb-api-query"
}

Step 3 — Agent signs and sends USDC on Base
(handled by x402 client library)
Step 4 — Agent retries with payment proof
GET /api/v1/businesses?zip=33601&category=plumber HTTP/1.1
X-Payment-Payload: eyJhbGci...signed.jwt.here...

HTTP/1.1 200 OK
X-Payment-Settled: true
→ data returned

The /.well-known/pay Discovery Endpoint

Agents don't need to know about payment up front. They discover it at the standard /.well-known/pay endpoint, which describes the payment configuration for the entire API.

curl https://support-local-businesses.com/.well-known/pay | jq .

The response looks like:

{
  "version": "1.0",
  "provider": "Support Local Businesses",
  "scheme": "x402",
  "network": "base",
  "chainId": 8453,
  "paymentReceiver": "0x0cF67aB1D0C843F67bC64D507A5627a41AE5BBC0",
  "asset": {
    "symbol": "USDC",
    "address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "decimals": 6
  },
  "pricing": {
    "default": { "amount": "0.001", "currency": "USDC", "per": "request" },
    "bulk_export": { "amount": "0.01", "currency": "USDC", "per": "request" }
  },
  "freeAllowance": {
    "requests": 100,
    "period": "daily",
    "resetTime": "00:00 UTC"
  },
  "discovery": {
    "mcp": "https://support-local-businesses.com/.well-known/mcp.json",
    "openapi": "https://support-local-businesses.com/openapi.json",
    "agent_card": "https://support-local-businesses.com/.well-known/agent.json"
  }
}

Code: Making a Micropayment as an Agent

Using the @x402/client library (Node.js):

import { wrapFetchWithPayment } from '@x402/client';
import { createWalletClient } from 'viem';
import { base } from 'viem/chains';
import { privateKeyToAccount } from 'viem/accounts';

// 1. Set up your Base wallet
const account = privateKeyToAccount(process.env.AGENT_PRIVATE_KEY);
const walletClient = createWalletClient({ account, chain: base });
// 2. Wrap fetch with automatic x402 handling
const payingFetch = wrapFetchWithPayment(fetch, walletClient);
// 3. Call SLB API — first 100/day are free, then auto-pays $0.001 USDC
const res = await payingFetch(
  'https://support-local-businesses.com/api/v1/businesses?zip=33601&category=restaurant&limit=20'
);
const data = await res.json();
console.log(Fetched ${data.businesses.length} restaurants in Tampa 33601);
// Fetched 20 restaurants in Tampa 33601

The wrapFetchWithPayment middleware handles the entire x402 handshake transparently: it detects 402 responses, signs the USDC transaction, and retries automatically.

Python equivalent

from x402.client import PaymentSession
from eth_account import Account

Load your Base wallet
account = Account.from_key(os.environ['AGENT_PRIVATE_KEY'])
session = PaymentSession(account=account, chain='base')

Call SLB — auto-pays when free tier exhausted
response = session.get(
    'https://support-local-businesses.com/api/v1/businesses',
    params={'zip': '33601', 'category': 'restaurant', 'limit': 20}
)
print(response.json()['businesses'])

Free Tier + Rate Limits

SLB runs a generous free tier before x402 kicks in:

Check your remaining free tier with response headers:

curl -I https://support-local-businesses.com/api/v1/businesses?zip=33601 \
  | grep -i "X-Free"

X-Free-Queries-Remaining: 87
X-Free-Queries-Limit: 100

Superfluid: Streaming Payments for Continuous Data

For agents that need continuous data streams (real-time business updates, live CRE alerts), pay-per-request gets expensive and slow. Enter Superfluid — programmable money streams on Base that flow by the second.

Instead of paying per query, your agent opens a stream:

import { Framework } from '@superfluid-finance/sdk-core';
import { ethers } from 'ethers';

const sf = await Framework.create({ chainId: 8453, provider });
// Open a stream to SLB at $1/day for continuous data access
const createFlowOperation = sf.cfaV1.createFlow({
  sender: agentWalletAddress,
  receiver: '0x0cF67aB1D0C843F67bC64D507A5627a41AE5BBC0', // SLB wallet
  superToken: USDCx_BASE_ADDRESS,
  flowRate: '11574074074074' // wei per second = ~$1/day in USDCx
});
await createFlowOperation.exec(signer);
// Agent now has continuous, metered access — no per-request overhead

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