x402-starters

# x402 starters

The shortest working way to charge for an HTTP route, and to pay for one, using the official
[x402](https://x402.org) SDKs. Every file here runs as it is; the only thing you must change is
the wallet that gets paid.

x402 revives HTTP `402 Payment Required`. Your server answers an unpaid request with `402` and
machine-readable terms, the client signs a stablecoin payment, and a facilitator verifies the
signature and settles it on-chain. Your server never holds a key and never talks to a chain.

## Pick one

| Folder | Stack | What it is |
|---|---|---|
| [`express`](express) | Node, Express | One paid `GET /premium` route |
| [`hono`](hono) | Node, Hono | The same route on Hono |
| [`next`](next) | Next.js App Router | A paid API route |
| [`fastapi`](fastapi) | Python, FastAPI | The same route in Python |
| [`client`](client) | Node and Python | Paying for a 402 route from a script or an agent |

## Run one in a minute

```bash
cd express
npm install
export MERCHANT=0xYourWalletAddress      # where the money goes, on Base
npm start
curl -i localhost:3000/premium           # 402 with terms
```

Then pay it with a client from [`client`](client), or point any x402 client at it.

## The facilitator

These starters use `https://pay.neuronto.com` as the facilitator: the service that verifies the payer's
signature and broadcasts the settlement. It is one line in every file, and any x402 facilitator
can take its place:

```js
new HTTPFacilitatorClient({ url: "https://pay.neuronto.com" })
```

Base mainnet (`eip155:8453`) is live there. `GET https://pay.neuronto.com/supported` lists every network,
scheme and version it settles right now; a network that cannot settle disappears from that list
before it starts refusing, so a server that reads `/supported` never advertises a price it
cannot take.

## Testing without spending anything

`https://pay.neuronto.com/echo` is a live merchant that charges $0.001 and **sends it straight back** in the
same request, so a client can be run end to end for the cost of nothing:

```bash
curl -i https://pay.neuronto.com/echo        # a real 402, with real terms
```

Point any of the clients in [`client`](client) at that URL. The refund is automatic; the gas is
not yours.

## What you need

- A wallet address to be paid to. Nothing is installed on your side to receive money: payments
  arrive as USDC transfers to the address you put in `MERCHANT`.
- For a paying client, a funded key. Never put a real key in a file: every example here reads it
  from the environment.

## Licence

Apache-2.0.