x402 Payments Skill

The most comprehensive x402 payments skill for AI coding agents. Teaches Claude Code, Codex, Cursor, Windsurf, and Gemini CLI how to build x402 payment infrastructure — not just consume it.

What it does

One install. Your AI agent knows how to:

• Monetize any API with x402 middleware (Next.js, Express, Hono)
• Call paid endpoints with automatic 402 payment handling
• Deploy on Base AND Solana with USDC
• Orchestrate multi-endpoint payments with @x402sentinel/router
• Generate unified cryptographic receipts with budget enforcement and audit trails

Quick Install

curl -sSL https://raw.githubusercontent.com/valeo-cash/x402-payments-skill/main/install.sh | bash

Auto-detects Claude Code, Codex CLI, and Cursor. Installs the skill to the right location.

Live Examples

Two ready-to-clone projects in examples/:

Seller: Paid Joke API

A Next.js API charging $0.001/request in USDC on Base Sepolia.

cd examples/paid-api-seller && npm install && npm run dev

Buyer: Pay for APIs

Node.js scripts that call paid endpoints — single and multi-endpoint with Sentinel Router.

cd examples/pay-for-api-buyer && npm install && npm run single

→ See all examples

What's Inside the Skill

The skill teaches your AI agent a decision tree:

User asks about x402 / paid APIs / agent payments
  │
  ├─ Are you the SELLER or BUYER?
  │   ├─ Seller → Server middleware setup
  │   └─ Buyer → Client fetch wrapper
  │
  ├─ Which CHAIN?
  │   ├─ Base (EVM) → x402-next / @x402/next
  │   ├─ Solana → x402-solana / @x402/svm
  │   └─ Both → V2 multi-chain registration
  │
  └─ Need MULTI-ENDPOINT orchestration?
      ├─ No → Basic x402 is enough
      └─ Yes → Sentinel Payment Router
              → Budget caps
              → Parallel execution
              → Unified cryptographic receipts

Full reference docs for every path: Base/EVM, Solana, Sentinel Router, and all 20+ npm packages in the x402 ecosystem.

Install

Claude.ai (Web / Mobile)

1. Download x402-payments.skill
2. Go to Settings → Skills
3. Upload the file

Claude Code (Plugin Marketplace)

/plugin marketplace add valeo-cash/x402-payments-skill

Claude Code (Manual)

git clone https://github.com/valeo-cash/x402-payments-skill.git
cp -r x402-payments-skill/x402-payments ~/.claude/skills/

Codex CLI

git clone https://github.com/valeo-cash/x402-payments-skill.git
cp -r x402-payments-skill/x402-payments ~/.codex/skills/

Cursor / Windsurf

Copy .cursorrules into your project root:

cp x402-payments-skill/.cursorrules ./

Per-project (shared via git)

cp -r x402-payments-skill/x402-payments .claude/skills/

What's inside

File	Purpose
SKILL.md	Main skill — decision tree, quick starts for seller/buyer on Base/Solana
references/base-evm.md	Complete Base/EVM server + client setup (V1 + V2 packages)
references/solana.md	Complete Solana server + client setup (Wallet Adapter, Privy, Node.js)
references/sentinel-router.md	Payment Router — multi-endpoint orchestration, budget caps, receipts
references/packages.md	Every x402 + Sentinel npm package with install commands
.cursorrules	Drop-in rules file for Cursor/Windsurf projects
examples/paid-api-seller/	Ready-to-deploy Next.js paid API (Vercel one-click)
examples/pay-for-api-buyer/	Node.js scripts for calling paid APIs + Sentinel Router

x402 Protocol

x402 is an open payment protocol by Coinbase using HTTP 402 status codes. Any API can charge per-request in USDC — no API keys, no subscriptions, no accounts. Works for humans and AI agents.

Sentinel Payment Router

@x402sentinel/router adds enterprise infrastructure on top of x402:

• Budget enforcement — set a cap before any money moves
• Parallel execution — pay multiple endpoints concurrently
• Unified receipts — SHA-256 hash + HMAC signature linking all payments
• Audit trails — cryptographic proof of what was paid, to whom, when

import { PaymentRouter } from "@x402sentinel/router";

const router = new PaymentRouter({
  paymentFetch: x402Fetch,
  getPaymentInfo: () => x402Fetch.getLastPayment?.() ?? null,
  agentId: "research-agent-01",
  apiKey: "sk_...",
});

const result = await router.execute({
  name: "research-pipeline",
  maxBudgetUsd: "0.10",
  strategy: "parallel",
  endpoints: [
    { label: "email-verify", url: "https://api.example.com/verify?email=test@gmail.com" },
    { label: "dns-lookup", url: "https://api.example.com/dns?domain=google.com" },
    { label: "ssl-check", url: "https://api.example.com/ssl?domain=google.com" },
  ],
});
// result.receipt → unified cryptographic proof of all 3 payments

Compatibility

Agent	Install method
Claude Code	/plugin marketplace add or ~/.claude/skills/
Codex CLI	~/.codex/skills/
Cursor	.cursorrules in project root
Windsurf	.cursorrules in project root
Gemini CLI	.claude/skills/ (same format)
OpenCode	.claude/skills/

Built by

Sentinel by Valeo — Audit and compliance infrastructure for AI agent payments.

License

MIT