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x402

Implement HTTP 402 stablecoin payments for APIs using ERC-3009 gasless USDC transfers.

1|1|Updated May 21, 2026
Search Tags:#agent commerce#micropayments#x402#coinbase#usdc payments#http-402#erc-3009
One-click install
npx skills add https://github.com/naruto11eth/cryptoskills --skill x402-naruto11eth
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: x402
Source: https://github.com/naruto11eth/cryptoskills/tree/main/skills/x402
Command: npx skills add https://github.com/naruto11eth/cryptoskills --skill x402-naruto11eth

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve? AI agents and API providers lack a native way to charge per-request without API keys, accounts, or billing systems, and LLMs frequently hallucinate outdated x402 details like wrong package names, header names, and nonce behavior. ## Core Features & Use Cases - Server Payment Middleware: Protect Express, Hono, or Next.js endpoints with per-route USDC pricing using @x402/express and the CDP facilitator. - Client Payment Flows: Wrap fetch in TypeScript or use the Python x402 package to automatically detect 402 responses, sign EIP-3009 authorizations, and retry with the X-PAYMENT header. - Agent-to-Agent Commerce: Discover paid agent services, enforce spending budgets, and orchestrate multi-step paid workflows across EVM chains and Solana. - Use Case: An AI agent needs weather data from a paid API. It sends a request, receives HTTP 402 with a $0.01 USDC price on Base, signs an EIP-712 transferWithAuthorization, retries with the X-PAYMENT header, and receives the data while the facilitator settles on-chain. ## Quick Start Use the x402 skill to add USDC payment middleware to my Express API endpoint on Base mainnet.

Frequently Asked Questions about x402

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I add USDC payments to my Express API with x402?▼

Install @x402/express, @x402/core, and @x402/evm, then apply paymentMiddleware with per-route pricing, network, and payTo address. Requests without a valid X-PAYMENT header receive HTTP 402 with payment requirements; valid payments are verified and settled via the facilitator.

How does x402 payment work without API keys?▼

Payment itself is authentication. The client signs an EIP-3009 transferWithAuthorization for USDC, includes it base64-encoded in the X-PAYMENT header, and the server verifies the signature and balance through a facilitator before serving the resource.

Which blockchains does x402 support?▼

x402 supports Base, Ethereum, Arbitrum, Optimism, and Polygon via USDC with EIP-3009, plus Solana. Networks are identified with CAIP-2 strings such as eip155:8453 for Base mainnet.

Why does x402 settlement fail with authorization is used or canceled?▼

The (from, nonce) pair was already consumed on-chain because a nonce was reused across payment attempts. Generate a fresh random 32-byte nonce for every authorization and check state with authorizationState on the USDC contract.

Does the client need ETH for gas when paying with x402?▼

No. The client only signs an off-chain EIP-712 authorization; the facilitator broadcasts transferWithAuthorization and pays gas. On Base mainnet, CDP's hosted facilitator absorbs gas costs for free-tier usage of 1,000 transactions per month.

Can x402 accept tokens other than USDC?▼

The primary path uses USDC via EIP-3009 for gasless transfers. A Permit2 fallback supports arbitrary ERC-20 tokens but requires a prior one-time approval transaction to the Permit2 contract, which needs native gas.

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