Shopify's Carrier Calculated Shipping API is needed for the app to work, allowing businesses to set rates by 20+ parameters to increase profits. This app offers rates per item and origin, accurate rates by postal code, zip code, and distance, product dimension based rates for custom products, rate blending to define how rates from different rule sets should be combined, and special rates by customer. It can be used in all countries supported by Shopify in the currency of their choice.