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HTTP 402 payment protocol for AI agent commerce — three-actor model (Client, Resource Server, Facilitator), ERC-3009 transferWithAuthorization, server middleware (@x402/express), client patterns in TypeScript and Python, facilitator integration, agent-to-agent payments, pricing strategies, and replay protection. Works on Base, Ethereum, Arbitrum, Optimism, Polygon, and Solana.
x402 is an open payment protocol that revives the HTTP 402 "Payment Required" status code to enable instant stablecoin payments directly over HTTP. It uses a three-actor model — Client (buyer), Resource Server (seller), and Facilitator (settlement) — to let any HTTP endpoint accept payment without API keys, sessions, or accounts. The protocol is built on EIP-3009 transferWithAuthorization for gasless USDC transfers, meaning clients sign an off-chain authorization and the facilitator broadcasts the on-chain settlement.
Package ecosystem:
@x402/express, @x402/hono, @x402/next@x402/fetch, @x402/axiospip install x402go get github.com/coinbase/x402/go@x402/core, @x402/evm, @x402/svmCDP Facilitator endpoint: https://api.cdp.coinbase.com/platform/v2/x402
LLMs have stale training data. These are the most common mistakes.
npx skills add 0xinit/cryptoskills --skill x402How clear and easy to understand the SKILL.md instructions are, rated from 1 to 5.
Clear and well structured, with only minor parts that might need a second read.
How directly an agent can act on the SKILL.md instructions, rated from 1 to 5.
Mostly actionable with clear steps; only a few small gaps remain.