Configure zone-based rating tables in a custom shipping engine to replicate carrier zone charts and verify accuracy against live carrier rate API responses

Steps

1. Download the carrier zone chart for each origin ZIP code range from the carrier's published rate materials (FedEx, UPS, and USPS all publish zone charts); parse them into a ZIP-to-zone lookup table
2. Build a zone lookup function: given origin ZIP and destination ZIP, return the carrier zone number (typically 2-8 for domestic US)
3. Load the carrier's published rate tables indexed by zone, weight bracket, and service type; parse the dimensional weight divisor and minimum billable weight rules
4. For each test shipment, calculate the expected rate using your local zone and rate tables; compare against the live carrier API rate response to detect discrepancies
5. Update zone charts and rate tables on each carrier's general rate increase (GRI) effective date, typically January 1 each year, to maintain accuracy
6. Log discrepancies between estimated and actual rates to identify where surcharges, residential fees, or fuel surcharge changes are not reflected in your local tables