Retrieving the Contents of a Cart

You should not maintain a local copy of the remote shopping cart. Instead, use CartGet to retrieve the items in a shopping cart.

Retrieving the items in a cart

Use the cart's HMAC and CartId values in a CartGet request.

http://ecs.amazonaws.com/onca/xml?
Service=AWSECommerceService&
AWSAccessKeyId=[AWS Access Key ID]&
AssociateTag=ws&
Operation=CartGet&
CartId=002-2041347-9034467&
HMAC=[HMAC]

By default, CartGet uses the Cart response group. This response group provides a lot of information about items, including, for example, their price, quantity, and the seller ID of the seller selling the item, as shown in the following response snippet.

<PurchaseURL>https://www.amazon.com/gp/cart/aws-merge.html?cart-id=002-9918938-1696046%26associate-id=ws%26hmac=b0ogzvivVYLXjSZ9WwoBRFesFYU=%26AWSAccessKeyId=[AWS Access Key ID]MergeCart=False</PurchaseURL>
<CartItems>
  <SubTotal>
    <Amount>1994</Amount>
    <CurrencyCode>USD</CurrencyCode>
    <FormattedPrice>$19.94</FormattedPrice>
  </SubTotal>
  <CartItem>
    <CartItemId>U3KYV0C66V3PAA</CartItemId>
    <ASIN>B000062TU1</ASIN>
    <MerchantId>ATVPDKIKX0DER</MerchantId>
    <SellerId>A2R2RITDJNW1Q6</SellerId>
    <SellerNickname>Amazon.com, LLC</SellerNickname>
    <Quantity>2</Quantity>
    <Title>Harry Potter and the Sorcerer's Stone (Full Screen Edition)(Harry Potter 1)</Title>
    <ProductGroup>DVD</ProductGroup>
    <Price>
      <Amount>997</Amount>
      <CurrencyCode>USD</CurrencyCode>
      <FormattedPrice>$9.97</FormattedPrice>
   </Price>
   <ItemTotal>
     <Amount>1994</Amount>
     <CurrencyCode>USD</CurrencyCode>
     <FormattedPrice>$19.94</FormattedPrice>
    </ItemTotal>
  </CartItem>
</CartItems>

You could, for example, use the CartItemId in a CartModify operation to change the quantity of that item. You could also use the PurchaseURL to purchase the items in the cart.