# What is x402? **x402** is an open standard for paying for an HTTP request with stablecoins. It is built on the long-reserved HTTP status code [`402 Payment Required`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/402). The idea is simple: an API can require a payment for a route. When a client calls that route without paying, the server replies `402` and describes exactly what is owed and to whom. The client signs a stablecoin payment off-chain, retries the request with a payment header, and the server lets it through once the payment is verified. It was designed for the agent economy. AI agents can't hold credit cards or complete checkout forms — but they can sign a stablecoin transfer and attach it to a request. x402 gives them a native, one-request-one-payment way to pay for APIs. ## What Parallel provides Parallel runs an **x402 facilitator** and ships drop-in middleware so any API can accept stablecoin payments in a few lines: * **Drop-in middleware** for Express, Next.js, Fastify, and Hono. * **Accepts USDp, USDC, and sUSDp** — the SDK routes the payment automatically. * **Zero platform fee** — Parallel takes no cut of your revenue. * **Gas sponsored** on Base, HyperEVM, and Avalanche. * **Settles directly to your wallet** — non-custodial, no Parallel account. * **MIT-licensed SDKs** — the middleware, the agent package and the CLI that signs its payments are published on npm. ## Start here - [Merchant quickstart — accept stablecoins in 5 minutes](/agents/x402/quickstart) - [Agent quickstart — build an agent that pays](/agents/x402/agent-quickstart) - [Concepts — how the facilitator works](/agents/x402/concepts) - [API reference](/agents/x402/api-reference) - [Migrate from Coinbase x402](/agents/recipes/migrate-from-coinbase-x402)