@checkoutkit/server

The merchant side of the Agentic Commerce Protocol. Implement one interface; the engine handles the protocol.

pnpm add @checkoutkit/server

import { createAcpServer } from "@checkoutkit/server";

const acp = createAcpServer({
  backend: {
    async createSession(input, ctx) { /* price items, compute totals */ },
    async getSession(id, ctx) { /* return null when unknown */ },
    async updateSession(id, patch, ctx) { /* re-price */ },
    async completeSession(id, payment, ctx) { /* charge, create order */ },
    async cancelSession(id, input, ctx) { /* release the cart */ },
  },
  auth: { verifyAgent: (req) => lookupAgent(req.headers.get("Authorization")) },
  signature: { hmacKeys: [process.env.ACP_HMAC_KEY!] },
  basePath: "/acp",
});

createAcpServer returns (req: Request) => Promise<Response>, so the same backend runs on Node, Bun, Deno, Cloudflare Workers and Vercel Edge. Framework adapters are thin wrappers: @checkoutkit/express, @checkoutkit/next, @checkoutkit/hono.

What it enforces for you

• HMAC request signatures, constant-time, with a replay window and key rotation
• Idempotency: required key, 409 in-flight, 422 conflict, replay marked with Idempotent-Replayed
• State transitions — completing a not_ready_for_payment session is rejected before your backend is called
• Totals arithmetic and response schema validation
• API-Version negotiation and spec-shaped errors

Anything your backend throws that is not an AcpError becomes an opaque 500, and payment tokens are redacted from every diagnostic path.

Running more than one instance? The default idempotency store is in-memory, so a retry landing on another replica charges twice. Use @checkoutkit/redis.

CheckoutKit is an independent community implementation of the Agentic Commerce Protocol. It is not affiliated with, sponsored by, or endorsed by OpenAI or Stripe.

Part of CheckoutKit · Apache-2.0