> For the complete documentation index, see [llms.txt](https://docs.peakcommerce.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.peakcommerce.com/developers/reference-pages/carts.md).

# Carts

Carts power on-page checkout flows. Unlike orders (which are atomic), carts let a session accumulate items and have promotions applied before being converted to an order.

> **Auth note:** cart endpoints sit behind the same API-key authentication as the rest of `/api/v1`. The `sessionId` you pass in is your storefront's own session identifier and scopes the cart for reuse — it does **not** authenticate the request. Send your tenant API key with every cart call.

* [`POST /api/v1/carts`](#post-apiv1carts) — get or create
* [`GET /api/v1/carts/{id}`](#get-apiv1cartsid)
* [`POST /api/v1/carts/{id}/items`](#post-apiv1cartsiditems)
* [`DELETE /api/v1/carts/{id}/items/{itemId}`](#delete-apiv1cartsiditemsitemid)
* [`POST /api/v1/carts/{id}/promo`](#post-apiv1cartsidpromo)
* [`DELETE /api/v1/carts/{id}/promo`](#delete-apiv1cartsidpromo)

***

## `POST /api/v1/carts`

Get or create a cart for a session. If a cart already exists for the `sessionId`, it is returned with its items.

### Body

| Field       | Type        | Required |
| ----------- | ----------- | -------- |
| `sessionId` | string (≥1) | yes      |

### Response `200` or `201`

```json
{
  "id": "cart_01H...",
  "tenantId": "ten_01H...",
  "sessionId": "sess_01H...",
  "status": "active",
  "subtotalCents": 0,
  "discountCents": 0,
  "totalCents": 0,
  "currency": "USD",
  "items": []
}
```

### cURL

```bash
curl -X POST https://api.example.com/api/v1/carts \
  -H "Authorization: Bearer $PEAK_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "sessionId": "sess_01H..." }'
```

***

## `GET /api/v1/carts/{id}`

Retrieve a cart with its items.

### Errors

| Status | When           |
| ------ | -------------- |
| `404`  | Cart not found |

### cURL

```bash
curl -H "Authorization: Bearer $PEAK_API_KEY" \
  https://api.example.com/api/v1/carts/cart_01H...
```

***

## `POST /api/v1/carts/{id}/items`

Add a line item. Recomputes subtotal, automatically re-evaluates auto- apply offers, and updates the discount/total.

### Body

| Field            | Type        | Required | Description                      |
| ---------------- | ----------- | -------- | -------------------------------- |
| `productId`      | UUID        | no       | Recommended; ties to the catalog |
| `offerId`        | UUID        | no       | Pre-applied offer ID             |
| `name`           | string      | yes      | Display name                     |
| `description`    | string      | no       |                                  |
| `quantity`       | integer ≥ 1 | no       | Defaults to 1                    |
| `unitPriceCents` | integer ≥ 0 | yes      |                                  |

### Response `201`

```json
{
  "id": "cart_01H...",
  "subtotalCents": 9800,
  "discountCents": 980,
  "totalCents": 8820,
  "currency": "USD",
  "items": [
    {
      "id": "ci_01H...",
      "cartId": "cart_01H...",
      "productId": "prod_01H...",
      "name": "Pro Plan",
      "quantity": 2,
      "unitPriceCents": 4900,
      "totalPriceCents": 9800,
      "currency": "USD"
    }
  ]
}
```

### cURL

```bash
curl -X POST https://api.example.com/api/v1/carts/cart_01H.../items \
  -H "Authorization: Bearer $PEAK_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "productId": "prod_uuid",
    "name": "Pro Plan",
    "quantity": 2,
    "unitPriceCents": 4900
  }'
```

***

## `DELETE /api/v1/carts/{id}/items/{itemId}`

Remove a line item; re-evaluates discounts and totals.

### Response `200`

Same shape as adding an item.

### cURL

```bash
curl -X DELETE https://api.example.com/api/v1/carts/cart_01H.../items/ci_01H... \
  -H "Authorization: Bearer $PEAK_API_KEY"
```

***

## `POST /api/v1/carts/{id}/promo`

Apply a promo code. Looks up the offer by code, validates against the current cart contents, and (if valid) attaches it.

### Body

| Field  | Type        | Required |
| ------ | ----------- | -------- |
| `code` | string (≥1) | yes      |

### Response `200`

```json
{
  "id": "cart_01H...",
  "subtotalCents": 9800,
  "discountCents": 980,
  "totalCents": 8820,
  "items": [ /* ... */ ],
  "offer": {
    "code": "WELCOME10",
    "name": "Welcome 10% off",
    "discountType": "percentage",
    "discountValue": "10",
    "discountAmountCents": 980
  }
}
```

### Errors

| Status | When                                                            |
| ------ | --------------------------------------------------------------- |
| `400`  | Offer invalid for this cart (expired, min-amount not met, etc.) |
| `404`  | Code not found                                                  |

### cURL

```bash
curl -X POST https://api.example.com/api/v1/carts/cart_01H.../promo \
  -H "Authorization: Bearer $PEAK_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "code": "WELCOME10" }'
```

***

## `DELETE /api/v1/carts/{id}/promo`

Remove the applied promo and recompute totals.

### Response `200`

Same shape as adding an item; `offer` field is absent.

### cURL

```bash
curl -X DELETE https://api.example.com/api/v1/carts/cart_01H.../promo \
  -H "Authorization: Bearer $PEAK_API_KEY"
```

***

## Related

* [Orders](/developers/reference-pages/orders.md) — convert a cart to an order
* [Pricing previews](/developers/reference-pages/pricing-previews.md)


---

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