This API signature is for testing purposes and will not generate usable labels and barcodes. The Request Parameter sections present the XML input tags for generating Live requests and the restrictions on the values allowed and returns requests for phone, zip, city, address and more. USPS Web Tools® API library enables external e-commerce shopping cart and shipping software to access USPS® data. From shipping rates to tracking information to scheduling a package pickup, Web Tools makes shipping with the U.S. Postal Service® easily accessible.