x402-client

name	x402-client
description	Make paid API requests using the x402 HTTP payment protocol (USDC on Base Sepolia). Use when you need to access x402-protected services, pay for API calls with crypto, or perform web searches via an x402 search gateway. Handles wallet setup, payment signing, and request retry automatically.

x402 Client

Make HTTP requests to x402-protected APIs. The x402 protocol uses HTTP 402 responses to request payment — this skill handles signing USDC payments and retrying automatically.

Prerequisites

• Node.js 18+ installed
• A Base Sepolia wallet with ETH (gas) and USDC (payments)

First-Time Setup

1. Install dependencies

bash <skill-dir>/scripts/setup.sh

This installs the x402 SDK to ~/.x402-client/. Only needed once.

2. Generate a wallet (if you don't have one)

node <skill-dir>/scripts/wallet-gen.mjs --out ~/.x402-client/wallet.key

3. Fund the wallet

Get testnet tokens from faucets:

• Base Sepolia ETH (gas): https://www.alchemy.com/faucets/base-sepolia
• Base Sepolia USDC (payments): https://faucet.circle.com/ → select Base Sepolia + USDC

Send both to the wallet address printed by wallet-gen.

4. Store the key

Set the environment variable for future use:

export X402_PRIVATE_KEY=$(cat ~/.x402-client/wallet.key)

Or pass --key-file ~/.x402-client/wallet.key to each request.

Making Paid Requests

Use x402-fetch.mjs to make any x402-paid HTTP request:

# Search the web ($0.001 USDC per query)
node <skill-dir>/scripts/x402-fetch.mjs \
  "https://<service-url>/web/search?q=latest+AI+news&count=5" \
  --key-file ~/.x402-client/wallet.key

The script automatically:

1. Makes the HTTP request
2. If 402 received, parses payment requirements
3. Signs a USDC payment with your wallet
4. Retries with the payment header
5. Outputs the response JSON to stdout

All scripts must be run from ~/.x402-client/ (where node_modules lives):

cd ~/.x402-client && node <skill-dir>/scripts/x402-fetch.mjs "<url>" --key-file wallet.key

Known Services

See references/services.md for a list of known x402 endpoints including a web search service.

Troubleshooting

• "insufficient funds": Wallet needs more USDC or ETH. Use faucets above.
• 402 with no auto-payment: Ensure setup.sh was run and you're executing from ~/.x402-client/.
• Tunnel URL not working: The service URL may have changed. Ask the service operator or check /health.