Harmonized System Codes, HS Codes, Tariff Codes; these are one of the many parameters on Customs Forms. These numbers are required on most Customs Forms for USPS, and some for FedEx, UPS, DHL, and others.
For a search of the proper HS Code for you items, you can search the HTS Online Reference Tool.
This is just one piece on automating your International shipments. The EasyPost API can help you automate this, as well as the rest of the Customs Forms, rating, purchasing as more. Our Shipping API provides to the following from FedEx, UPS, USPS, DHL, and more:
To learn more you can take a look at our Customs Forms Documentation to see how simple the integration is.