@countersign/x402

@countersign/x402

Govern x402 (HTTP-402 machine payments) with Countersign — guard an agent's payment against policy before it pays.

When an agent hits a 402 Payment Required challenge, route it through Countersign's pre-flight spend guard first: parse the challenge → evaluate against one unified policy (per-call caps + payee allowlist

• daily metering, fail-closed) → only hand off to the wallet/x402 client if allowed. Countersign decides; it never signs or moves funds.

import { parseX402, withX402Guard } from "@countersign/x402";
import { CountersignClient } from "@countersign/sdk";

const cs = new CountersignClient({ baseUrl, apiKey });

// `challenge` is the 402 response body ({ accepts: [...] }).
const charge = parseX402(challenge);            // cheapest acceptable option, normalized
if (charge) {
  // Only pays if Countersign allows — a rogue or over-budget agent never pays.
  await withX402Guard(cs, agentId, charge, (c) => payWithYourX402Client(c));
}

• parseX402(body) — normalize a 402 challenge to a single charge (cheapest option, base units).
• guardX402(api, agentId, charge) — ask Countersign: allow / deny / needs_approval.
• withX402Guard(api, agentId, charge, pay) — evaluate, then run pay only on allow; throws X402Denied otherwise.

Apache-2.0. Pairs with @countersign/sdk and @countersign/mcp.