How an Agent Pays a Per-Request API with x402 and USDC on Base

x402 turns HTTP 402 Payment Required into a machine-readable price. Here is switch402's real 402 response and the code an agent uses to pay it and get the page.

Steps

1. Call without payment. POST https://api.switch402.com/v1/scrape with {"url": "..."}. The API answers HTTP 402 with the payment terms in the JSON body and in a base64 PAYMENT-REQUIRED header.
2. Read the terms. accepts[0] says: scheme exact, network eip155:8453 (Base), asset USDC, amount 8000 (6 decimals = $0.008), maxTimeoutSeconds 60.
3. Sign and retry. An x402 client signs a USDC transfer authorization for that amount and repeats the request with the payment header.
4. Get the result. The payment is verified, the page is fetched, and the payment settles only after content comes back. If every provider fails you get a 502 and pay nothing.

Code

HTTP/2 402
content-type: application/json
payment-required: <base64 of the same JSON>

{
  "x402Version": 2,
  "error": "Payment required",
  "resource": { "url": "https://api.switch402.com/v1/scrape", "mimeType": "application/json" },
  "accepts": [{
    "scheme": "exact",
    "network": "eip155:8453",
    "amount": "8000",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "payTo": "<payee address from the live response>",
    "maxTimeoutSeconds": 60,
    "extra": { "name": "USD Coin", "version": "2" }
  }]
}

curl -i -X POST https://api.switch402.com/v1/scrape \
  -H 'Content-Type: application/json' -H 'User-Agent: my-agent/1.0' \
  -d '{"url":"https://example.com"}'

// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPaymentFromConfig } from '@x402/fetch'
import { ExactEvmScheme } from '@x402/evm'
import { privateKeyToAccount } from 'viem/accounts'

const account = privateKeyToAccount(process.env.AGENT_KEY)
const fetchWithPayment = wrapFetchWithPaymentFromConfig(fetch, {
  schemes: [{ network: 'eip155:8453', client: new ExactEvmScheme(account) }],
})
const res = await fetchWithPayment('https://api.switch402.com/v1/scrape', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json', 'User-Agent': 'my-agent/1.0' },
  body: JSON.stringify({ url: 'https://example.com' }),
})
console.log(res.status, (await res.json()).markdown)

You pay only for the pages you actually fetch: $0.008 per standard page on /v1/scrape, $0.003 per lite call on /v1/scrape/lite, in USDC on Base and charged only on success. No subscription or unused credits; optional prepaid packs and a $10 monthly plan.