How do I pay for and call a P0 route from JavaScript, Python or LangChain?

JavaScript: @x402/fetch

npm install @x402/fetch @x402/core @x402/evm viem

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

// Your own wallet key, from the environment. It stays on your machine.
const signer = privateKeyToAccount(process.env.EVM_PRIVATE_KEY);
const client = new x402Client();
client.register("eip155:*", new ExactEvmScheme(signer));
const fetchWithPayment = wrapFetchWithPayment(fetch, client);

// The first request gets HTTP 402; the wrapper signs the payment and retries.
const response = await fetchWithPayment("https://x402-bazaar-rank.x402-bazaar-rank-worker.workers.dev/vuln/cve?id=CVE-2021-44228", { method: "GET" });
console.log(response.status, await response.json());

wrapFetchWithPayment wraps fetch; the wallet is a viem account. Replace the URL with any paid route of this site.

Python: official x402 client (requests)

pip install "x402[requests]" eth_account

import os
from urllib.parse import urlencode

from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

BASE = "https://x402-bazaar-rank.x402-bazaar-rank-worker.workers.dev"

client = x402ClientSync()
# Your own wallet key, from the environment. It stays on your machine.
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.getenv("EVM_PRIVATE_KEY"))))


def p0_cve(cve_id: str) -> dict:
    """Pay for and fetch one CVE triage from P0 (path /vuln/cve)."""
    with x402_requests(client) as session:
        response = session.get(BASE + "/vuln/cve?" + urlencode({"id": cve_id}))
        response.raise_for_status()
        return response.json()


if __name__ == "__main__":
    print(p0_cve("CVE-2021-44228"))

x402ClientSync and x402_requests are the synchronous client; the same package has an httpx (async) client, see the quickstart.

LangChain: a tool around the Python function

pip install langchain  # plus the Python snippet above

from langchain.tools import tool

# p0_cve is the function from the Python snippet above (save it as p0_client.py).
from p0_client import p0_cve


@tool
def cve_triage(cve_id: str) -> dict:
    """Triage one CVE: CVSS score, EPSS exploit probability and CISA KEV status. Paid per call over x402."""
    return p0_cve(cve_id)


# Give cve_triage to your agent in its list of tools, as described in the LangChain Tools guide.

A plain @tool function that calls p0_cve; the payment happens inside the call.

Before you run it

• The snippets follow the official x402 quickstart for buyers, read on 2026-10-25; P0 does not run them with a live payment on this page, and the page tests check their syntax only.
• The wallet must hold USDC on a network P0 accepts over x402 (USDC on Base, Arbitrum, Polygon, Avalanche, Optimism, Celo, Ethereum; USDT0 on Arbitrum; sBTC on Stacks). The snippets register EVM networks (eip155:*); for Solana and other chains add the matching package from the quickstart.
• No account, API key or sign-up is needed. Bad input is refused before any charge. No x402 client? Pay by a direct transfer and claim it with the transaction hash: https://x402-bazaar-rank.x402-bazaar-rank-worker.workers.dev/pay.
• Swap the path and parameters for any other paid route listed in https://x402-bazaar-rank.x402-bazaar-rank-worker.workers.dev/openapi.json.

Related

• /answers/pay-api-with-x402
• /answers/cve-epss-kev-priority
• /pay
• /openapi.json