x402 Coinbase Buyer Demo

Coinbase-first x402 buyer demo with Across pre-funding.

What Lives Here

• src/buyer/ contains the x402 buyer flow and Across funding logic.
• src/demo/ contains the runnable buyer demo entrypoint.
• src/dev/ contains local-only helpers and the local x402 seller.

Wallet Surface

The demo uses a Coinbase CDP server wallet via @coinbase/cdp-sdk. The buyer's private key never leaves Coinbase infrastructure — signing happens via the CDP API.

The wallet is resolved through src/buyer/coinbase-wallet.ts, which calls cdp.evm.getOrCreateAccount({ name: 'x402-buyer' }) to create or retrieve a persistent server-managed wallet.

Environment

• CDP_API_KEY_ID — CDP API key ID
• CDP_API_KEY_SECRET — CDP API key secret
• CDP_WALLET_SECRET — CDP wallet secret (required for signing)
• MERCHANT_KEY — merchant private key (local seller only)
• PORT

Create a local .env.local in this folder:

cp .env.example .env.local

Commands

npm install
npm run preflight
npm run demo:local
npm run demo:local:strict
npm run demo:external
npm run dev:server

Notes

• Mainnet target is Base (eip155:8453).
• The x402 seller requires CDP credentials for verify and settlement.
• The buyer does not reimplement x402; it funds first, then lets the x402 SDK create the payment payload and replay the request.
• demo:local uses the local seller by default.
• demo:external targets the CoinGecko x402 endpoint.