x402-agent-wallet

npm install x402-agent-wallet

The problem

Give an agent a funded wallet and an x402 client and it can spend money in a loop, at machine speed, with no human in the path. The failure modes are not exotic: a retry storm on a $0.05 endpoint, a prompt-injected merchant, a pricing bug that turns $0.001 into $1.00.

maxValue in x402-fetch caps a single payment. That is not a budget. This is the budget — plus the caps, the allowlists, the approval threshold, and a signed record of every decision.

Enforce it client-side

import { wrapPayerFetch, PolicyViolationError } from "x402-agent-wallet";
import { createSigner } from "x402-fetch";

const payFetch = wrapPayerFetch(fetch, {
  signer: {
    evm: await createSigner("base-sepolia", process.env.EVM_KEY!),
    svm: await createSigner("solana", process.env.SOLANA_KEY!),
  },
  policy: {
    dailyBudgetUsd: 1,
    perRequestMaxUsd: 0.05,
    perMerchantDailyUsd: { "api.example.com": 0.25 },
    perRailDailyUsd: { solana: 0.5 },
    approvalThresholdUsd: 0.02,
    preferRail: "evm",
  },
});

await payFetch("https://api.example.com/paid");   // PolicyViolationError if blocked

Or run the daemon

*requires X-Admin-Key. A denial is a 200 with allowed: false — you paid for the answer, and "no" is the answer.

Rail-aware, end to end

allowedRails gates which chains the agent may touch, perRailDailyUsd caps each independently, preferRail picks when both are offered, and the ledger reports spentTodayByRail. On Solana the facilitator sponsors the network fee, so the agent needs only USDC — no SOL.

Docs