Agent x402 Guide

This guide gets an AI agent set up to make x402 payments. Three steps: install, wallet, go.

For how x402 works under the hood, see x402.

1. Install Dependencies

npm install @x402/fetch @x402/evm viem

• viem — wallet creation and EIP-712 signing
• @x402/evm — EVM payment scheme for x402
• @x402/fetch — wraps fetch to handle 402 responses automatically

2. Set Up a Wallet

You need an EVM private key for a wallet with USDC on Base (chain ID 8453). If you already have one, skip to step 3 — set it as WALLET_PRIVATE_KEY in your environment.

To create a new wallet:

import { generatePrivateKey, privateKeyToAccount } from "viem/accounts";

const privateKey = generatePrivateKey();
const signer = privateKeyToAccount(privateKey);

console.log("Address:", signer.address);
console.log("Private key:", privateKey);

Fund this wallet with USDC on Base before proceeding.

Any wallet that can sign EIP-712 typed data works — the raw private key approach above is the simplest. Coinbase Agentic Wallet is an alternative with native x402 support and programmable spending limits.

3. Make a Paid Request

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

const signer = privateKeyToAccount(process.env.WALLET_PRIVATE_KEY as `0x${string}`);
const client = new x402Client();
registerExactEvmScheme(client, { signer });
const fetchWithPayment = wrapFetchWithPayment(fetch, client);

fetchWithPayment works like a normal fetch. When a server responds with HTTP 402, it automatically signs the USDC authorization, retries with proof, and returns the result. Use it on any x402 endpoint:

const response = await fetchWithPayment("https://api.aixbt.tech/x402/v2/api-keys/1d", {
  method: "POST",
});

const { data } = await response.json();