x402plus

Pay for any API, from any chain, with one signature.

x402plus extends the x402 protocol with multi-chain support (EVM, Solana, Movement) and intent-based gasless payments via Stableyard GRID ID.

x402       GET /api -> 402 -> sign USDC transfer -> pay on-chain -> 200
x402plus   GET /api -> 402 -> sign intent        -> settle off-chain -> 200

Install

npm install @stableyard/x402plus

Backend — monetize an API in 2 lines

import { x402plus } from "@stableyard/x402plus";

app.use(x402plus("0xYourAddress", {
  "GET /api/premium":    0.10,   // $0.10 per request
  "POST /api/generate":  5.00,   // $5.00 per generation
}));

No facilitator URL needed. No USDC addresses. No chain config. Just a wallet address and dollar amounts.

Multi-chain support

app.use(x402plus("0xYourAddress", {
  "GET /api/premium": 0.10,
}, {
  defaultChain: "polygon",
  solana: { payTo: "YourSolanaAddress" },
  movement: { payTo: "0x00...YourMovementAddress" },
}));

Custom facilitator

app.use(x402plus("0xYourAddress", routes, "https://your-facilitator.com"));

Client — pay for an API

import { withPayments } from "@stableyard/x402plus/client";

const paidFetch = withPayments(window.ethereum);
const res = await paidFetch("https://api.example.com/premium");

Payment schemes

Every 402 response offers multiple schemes. Clients choose based on what they have:

| | exact EVM | exact Solana | exact Movement | intent (GRID ID) | |---|---|---|---|---| | Signs | EIP-3009 | Solana Transaction | Aptos BCS | EIP-712 intent | | Settlement | On-chain | On-chain | On-chain | Off-chain | | Gas | Facilitator pays | Facilitator pays | Payer pays | Zero |

Networks

| Network | Exact | Intent | Asset | |---------|-------|--------|-------| | Ethereum, Base, Polygon, Arbitrum, Optimism | Yes | Yes | USDC | | Solana, Solana Devnet | Yes | -- | USDC / SOL | | Movement, Movement Testnet | Yes | -- | USDC.e / MOVE |

Exports

// Middleware (backend)
import { x402plus } from "@stableyard/x402plus";

// Client (frontend)
import { withPayments, createGridClient } from "@stableyard/x402plus/client";

// Types
import type { PaymentRequirements, Signer } from "@stableyard/x402plus/types";

// Facilitator client
import { createHttpFacilitatorClient } from "@stableyard/x402plus/facilitator";

Debug

Set DEBUG_X402=true to enable verbose logging.

Links

• x402.org — The base x402 protocol
• Stableyard — GRID ID infrastructure
• Integration Guide

License

Apache-2.0