> ## Documentation Index
> Fetch the complete documentation index at: https://docs.stateset.com/llms.txt
> Use this file to discover all available pages before exploring further.

# ACP Overview

> The Agentic Commerce Protocol — how an agent completes a real checkout inside a conversation.

# ACP Overview

The **Agentic Commerce Protocol** is OpenAI's specification for ChatGPT Instant Checkout. It lets
an AI agent take a buyer from conversation to completed order without leaving the chat — while
orders, payments, and compliance stay on your existing commerce stack.

This is the "rails" half of [what StateSet builds](/why-stateset): the engine an agent runs on,
and the protocol it transacts over.

## Two specifications

The handler implements both halves:

| Spec                  | What it covers                             |
| --------------------- | ------------------------------------------ |
| **Agentic Checkout**  | The merchant checkout API — five endpoints |
| **Delegated Payment** | PSP payment vault integration              |

Delegated payment is what makes this safe: the agent never handles raw card details. A vaulted
credential is passed to your payment provider, which authorises it.

## The flow

```
 Buyer in ChatGPT
      │  "order me another bag of the dog food"
      ▼
   Agent ──▶ POST /checkout_sessions          create
         ──▶ POST /checkout_sessions/:id      update — address, shipping, promo
         ──▶ POST /agentic_commerce/delegate_payment
         ──▶ POST /checkout_sessions/:id/complete
                        │
                        ▼
              order created in your stack
                        │
                        ▼
              fulfillment / ERP
```

Each step is a deterministic API call with a defined response, so an agent can drive it without
bespoke per-merchant logic.

## Components

| Piece                 | Role                                                                                                              |
| --------------------- | ----------------------------------------------------------------------------------------------------------------- |
| **ACP handler**       | Terminates the protocol; a standalone Rust server                                                                 |
| **Embedded engine**   | [iCommerce](/stateset-icommerce/stateset-icommerce-quickstart) in-process, so a session really reserves inventory |
| **Sync Server**       | Validation, routing, orchestration to downstream systems                                                          |
| **Fulfillment / ERP** | Execution and tracking                                                                                            |

<Note>
  The handler carries the commerce engine **in the same process**. There's no control plane and no
  network hop between the protocol and the thing that fulfils it — which is why a completed session
  produces a real order rather than a queued request.
</Note>

## What it enables

* **Conversational commerce** across ChatGPT, Claude, and custom agents.
* **Automated purchasing and reorders** — an agent can reorder without a human touching a
  checkout form.
* **One API across channels**, rather than an integration per assistant.

## Compliance is testable

ACP is a spec, so conformance is a fact rather than an opinion:

```bash theme={null}
npx acp-conformance --url <handler-url> --api-key <key>
```

The reference implementation ships a spec-compliance matrix documenting exactly which
requirements are met.

## How ACP relates to UCP and ICP

| Protocol                 | Scope                                                                                         |
| ------------------------ | --------------------------------------------------------------------------------------------- |
| **ACP**                  | ChatGPT Instant Checkout — sessions plus delegated payment                                    |
| [**UCP**](/stateset-ucp) | Platform-neutral checkout interop — discovery, tokenization, OAuth, AP2                       |
| [**ICP**](/stateset-icp) | The superset — agent identity, mandates, negotiation, returns, subscriptions, global commerce |

ACP is the right target when your buyers are in ChatGPT. ICP subsumes it when you need agent
identity, budgets, or peer-to-peer agent commerce.

## Related

* [ACP Quickstart](/stateset-acp/stateset-acp-quickstart)
* [Checkout guide](/agentic-commerce/agentic-commerce-checkout-guide)
* [ACP Reference](/stateset-acp/stateset-acp-endpoints)