x402 Payment Skill

Pay for resources using the x402 HTTP payment protocol. Enables agents to pay for compute, domains, APIs, and other services using USDC on Base — no accounts, no KYC, just cryptographic identity.

What is x402?

HTTP 402 "Payment Required" was reserved in the original HTTP spec but never standardized. The x402 protocol implements it for machine-to-machine payments:

1. Request a paid resource → get HTTP 402 + payment requirements
2. Sign an EIP-3009 transferWithAuthorization (gasless USDC transfer)
3. Resubmit with X-Payment header containing the signed authorization
4. Payment verified on-chain → resource granted

No API keys. No accounts. Pure wallet → payment → access.

Prerequisites

• An Ethereum wallet with private key
• USDC on Base (chain ID 8453)
• Node.js with viem installed

Usage

Basic x402 Fetch

import { x402Fetch } from './x402.mjs';
import { privateKeyToAccount } from 'viem/accounts';

// Load your wallet (NEVER hardcode keys!)
const account = privateKeyToAccount(process.env.PRIVATE_KEY);

// Fetch with automatic x402 payment
const response = await x402Fetch(account, 'https://api.example.com/paid-resource');
const data = await response.json();

Manual Payment Flow

For more control, use the individual functions:

import { parsePaymentRequired, createPaymentSignature, encodePaymentHeader } from './x402.mjs';

// 1. Make initial request
const response = await fetch(url);

if (response.status === 402) {
  // 2. Parse payment requirements
  const requirements = await parsePaymentRequired(response);
  
  // 3. Find supported option (Base USDC)
  const option = requirements.accepts.find(
    a => a.scheme === 'exact' && a.network === 'eip155:8453'
  );
  
  // 4. Sign payment
  const payment = await createPaymentSignature(account, option, requirements.x402Version);
  
  // 5. Retry with payment header
  const paidResponse = await fetch(url, {
    headers: { 'X-Payment': encodePaymentHeader(payment) }
  });
}

Scripts

x402.mjs — Core Library

The main x402 implementation. Functions:

• parsePaymentRequired(response) — Parse 402 response for payment requirements
• createPaymentSignature(account, requirement, version) — Sign EIP-3009 authorization
• encodePaymentHeader(payload) — Base64 encode for X-Payment header
• x402Fetch(account, url, options) — Fetch with automatic payment handling

conway-credits.mjs — Conway Compute Credits

Top up Conway compute credits:

PRIVATE_KEY=0x... node conway-credits.mjs 5
# Tops up $5 in Conway credits

conway-domain.mjs — Conway Domain Registration

Register domains via Conway:

PRIVATE_KEY=0x... node conway-domain.mjs example.com

Wallet Security

NEVER commit private keys to version control.

Recommended patterns:

• Environment variables: process.env.PRIVATE_KEY
• Secure file with restricted permissions: chmod 600 wallet.json
• Hardware wallet via WalletConnect (advanced)

Supported Networks

Network	Chain ID	USDC Address
Base	8453	0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913
Base Sepolia	84532	0x036CbD53842c5426634e7929541eC2318f3dCF7e

Known x402 Providers

• Conway — Compute, inference, domains (conway.tech)
• Farcaster Hub — Some hubs accept x402 for API access

References

• x402 Protocol Spec
• EIP-3009: Transfer With Authorization
• Conway Documentation

Author

Built by Lumen — March 2026

First successful x402 payment: TX 0xba5eaf2e4f1c7b9f79581c1771adc2527b2029dbbc900c429d3f69eafe6d3ba7