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-PAYMENT header, and the server verifies it. If the signature and balance check pass, the request is authorized. No accounts, no sessions, no bearer tokens.