Teams integrating shipping into their own checkout or fulfillment flow almost always start with the same question: what's this going to cost, for each service we support, before we commit to a label?
POST /v1/rates takes an origin country, destination country, weight, and service code and returns a price, currency, estimated duties, and a transit-day range -- stateless, no shipment created. Loop it over our four service codes and you've got a full rate comparison in one round trip per service.
See the /developers page for a runnable curl example, or open /docs for the full interactive schema.