# cartLinesAdd

Adds merchandise lines to an existing cart

## Authentication

> **Public Access**: Accessible with the public API key

## Mutation Structure

```graphql
mutation {
  cartLinesAdd(id: String!, lines: [CartLineInput!]!) {
    cart {
      # Cart fields
    }
    userErrors {
      # UserError fields
    }
  }
}
```

## Input Arguments

| Argument | Type | Required | Description |
|----------|------|----------|-------------|
| id | String! | Yes | The ID of the cart to add lines to |
| lines | [CartLineInput!]! | Yes | The input for adding lines to the cart |

## Return Type

[CartLinesAddPayload](/reference/storefront/v1/objects/cart-lines-add-payload) - Payload returned by the cartLinesAdd mutation. Returns an updated cart object and a list of user errors if any occurred during the operation.

## Example

```graphql
mutation {
  cartLinesAdd(
    id: "eyJhbGciOiJIUzI1NiJ9..."
    lines: [
      {
        merchandiseId: "12345"
        quantity: 2
      }
    ]
  ) {
    cart {
      id
      lines {
        nodes {
          id
          quantity
        }
      }
    }
    userErrors {
      field
      message
    }
  }
}
```

## Related Types

- [CartLinesAddPayload](/reference/storefront/v1/objects/cart-lines-add-payload)
- [CartLineInput](/reference/storefront/v1/inputs/cart-line-input)