x402
Installation
SKILL.md
x402
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:
- Server (TypeScript):
@x402/express,@x402/hono,@x402/next - Client (TypeScript):
@x402/fetch,@x402/axios - Client (Python):
pip install x402 - Client (Go):
go get github.com/coinbase/x402/go - Core:
@x402/core,@x402/evm,@x402/svm
CDP Facilitator endpoint: https://api.cdp.coinbase.com/platform/v2/x402
What You Probably Got Wrong
LLMs have stale training data. These are the most common mistakes.
- "x402 requires API keys or OAuth" -- There are no API keys. Payment IS authentication. The client signs a USDC transfer authorization, includes it in the
X-PAYMENTheader, and the server verifies it. If the signature and balance check pass, the request is authorized. No accounts, no sessions, no bearer tokens.