Give your agent a budget, not your keys.

1Create a vault

From the factory, in the token your agent pays with. maxFeeBps is the highest fee you accept; the pilot fee is 0.

// one vault per agent (or per budget)
vault = factory.createVault(token, /* maxFeeBps */ 0)
token.approve(vault, amount); vault.deposit(amount)

2Set the leash, then switch it on

Every vault starts paused, with the payee allowlist on.

vault.setAgent(agentAddress)                  // the only key your agent holds
vault.setPolicy(perPayment, per24h, true)     // caps in token units · allowlist on
vault.setPayee(weatherApi, true)              // approve who may be paid
vault.setPaused(false)

3Pay inside an x402 request

When an API answers 402 Payment Required, check the leash for free, pay once, then retry with the receipt.

// agent side (proposed pseudocode; adapter not published yet)
res = fetch(url)
if (res.status == 402) {
  req = res.json().accepts[0]                         // payTo, asset, amount, nonce
  ref = keccak256(chain, asset, payTo, resource, amount, nonce)
  [ok, reason] = vault.canPay(req.payTo, req.amount, ref)
  if (!ok) return stop(reason)                        // e.g. DailyLimitExceeded
  tx = vault.pay(req.payTo, req.amount, ref)
  res = fetch(url, { headers: { 'X-PAYMENT': base64({ nonce, tx }) } })
}

4Seller side: trust the receipt

Before serving data, the proposed seller adapter must check the transaction:

• It succeeded and has enough confirmations.
• The Paid event comes from a vault the factory created (factory.isVault), in the right token.
• Payee, amount and ref match the request; the nonce is used once.