USPS Rates & Labels
Add-on ID: kv_usps_v3 · Edition: CS-Cart & Multi-Vendor · Latest version: 1.0.0 · Compatible with: CS-Cart & Multi-Vendor 4.17.2 – 4.21.x, PHP 7.4 – 8.3 · Changelog: view
USPS Rates & Labels connects CS-Cart to the new USPS APIs platform (apis.usps.com, OAuth 2.0). It shows live USPS prices and delivery estimates at checkout and prints USPS labels from the order page.
USPS retired its old Web Tools API on 25 January 2026. The built-in USPS module of CS-Cart 4.17 and 4.18 still calls Web Tools, so it no longer returns rates; CS-Cart 4.21 added a new rates-only USPS module, and no CS-Cart version prints USPS labels. This add-on works on all of them, next to the 4.21 module, with your own USPS credentials: no aggregator account and no per-label fee. You pay USPS postage only.
- Live rates. One Shipping Options request per package returns every USPS service with price and delivery commitment; each USPS shipping method at checkout uses the service you picked for it. Responses are cached, so several USPS methods cost one request.
- Services. USPS Ground Advantage, Priority Mail, Priority Mail Express, Media Mail, Library Mail, Bound Printed Matter, the Priority Mail Flat Rate Envelopes and Small / Medium / Large Flat Rate Boxes; First-Class Package International Service, Priority Mail International (with flat rate boxes), Priority Mail Express International and Global Express Guaranteed (rates only).
- Your pricing rules. Retail, commercial or contract prices, markup in percent and/or a fixed amount, rounding up, a free shipping threshold, and a fallback rate when USPS cannot be reached.
- Packaging. Box presets with inside size, packaging weight and maximum load, automatic choice of the smallest box that carries the weight, product box sizes from CS-Cart, dimensional weight shown before you buy.
- Labels. Domestic and international labels (PDF, ZPL 203/300 dpi or PNG; 4x6, 4x5, 4x4, 6x4) from the order’s USPS tab, with a rate quote first, Signature Confirmation, insurance and customs forms. The tracking number goes onto a new CS-Cart shipment automatically.
- Void and refund. Unused labels are cancelled; labels already in a USPS shipping file get a refund request with its dispute ID.
- Tracking. Status and scan events on the order page and in the customer account, updated by cron, with an optional order status when everything is delivered.
- Address validation. USPS standardized addresses (ZIP+4) as a suggestion at checkout and on the order page.
- Multi-Vendor. The marketplace buys every label, or each vendor connects its own USPS account and buys labels in the vendor panel. Vendors’ products are priced from the vendor’s own ZIP Code.
Documentation
Section titled “Documentation”| Page | Contents |
|---|---|
| Installation | Requirements, USPS registration, installing, cron, upgrading, uninstalling |
| Configuration | USPS account, settings, shipping methods, box presets, Multi-Vendor |
| Usage | Checkout, buying labels, printing, tracking, void and refund, address validation |
| Developer notes | USPS API flow, data model, hooks, test mock, file map |
| FAQ | Common questions |
USPS is a trademark of the United States Postal Service. This add-on is not affiliated with or endorsed by USPS.