Skill: Cross-asset price monitor

Side-by-side snapshot of a stock and a crypto asset: the equity's latest close against a live crypto quote, a trailing-year series for each, and a date-stamped comparison. Send POST /api/skill/price-monitor with the required fields ticker and coin and pay $0.021 per call over x402 or MPP (there is no free tier). It returns a JSON object with pack, args, steps and summary.

Cross-asset price monitor skill pack: one x402 payment runs 5 underlying tools (stock-quote, stock-history, crypto-price, crypto-history, date-format); partial-success per step.

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/skill/price-monitor \
  -H "Content-Type: application/json" \
  -d '{"ticker":"AAPL","coin":"bitcoin"}'

Without payment this returns HTTP 402 Payment Required with the exact price for skill-price-monitor; any x402 v2 or MPP client pays it and retries.

Example response

{
  "pack": "price-monitor",
  "args": {
    "ticker": "AAPL",
    "coin": "bitcoin"
  },
  "steps": [
    {
      "slug": "stock-quote",
      "ok": true,
      "result": {}
    },
    {
      "slug": "stock-history",
      "ok": true,
      "result": {}
    },
    {
      "slug": "crypto-price",
      "ok": true,
      "result": {}
    },
    {
      "slug": "crypto-history",
      "ok": true,
      "result": {}
    },
    {
      "slug": "date-format",
      "ok": true,
      "result": {}
    }
  ],
  "summary": "5/5 steps succeeded"
}

From an MCP client

catalog.call {
  "slug": "skill-price-monitor",
  "params": {
    "ticker": "AAPL",
    "coin": "bitcoin"
  }
}

The hosted connector at https://agent402.tools/mcp needs a payment for skill-price-monitor; the stdio package pays it from a wallet or from an AGENT402_CREDITS_KEY issued earlier. Local install: npx -y [email protected].

Errors and behavior

• Arguments left out fall back to the pack's own defaults. Each step reports on its own; the call succeeds when at least one step does, and a run where every step fails is refused (400 when the input caused it, 502 otherwise).
• A paid call that ends in any status of 400 or above is not charged over x402, MPP or a prepaid credits key: settlement runs after the tool and only on a successful response. The exception is a Tempo push credential, a transfer the buyer sent before the call: it settles before the tool runs, so if the tool then fails the payment is recorded as a refund owed to the paying wallet.
• Wallet-only: this tool reaches the network or stored state, so it has no proof-of-work tier. A prepaid card-credits key issued earlier (Authorization: Bearer a402_...) also pays it.
• A GET or HEAD to /api/skill/price-monitor returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB is not replayed).

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
client.setSpendControls?.({ maxAmountPerPayment: "$0.021" }); // refuse any quote above this tool's price
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/skill/price-monitor", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "ticker": "AAPL",
    "coin": "bitcoin"
  }),
});

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