USPS API Integration for eCommerce, Shipping, and Fulfilment Platforms.

The USPS Web Tools XML API was fully retired on January 25, 2026, meaning any calls to it are failing or returning degraded responses. Migration to the new USPS REST API is required immediately. The new API uses OAuth 2.0 instead of the old USERID parameter, JSON instead of XML, and separate versioned endpoints per resource. You cannot simply update the endpoint URL: the authentication method, request format, and response parsing all need to be rebuilt. We handle the full migration: mapping your existing XML calls to the equivalent REST endpoints, rebuilding the authentication layer, updating response parsers, and testing end-to-end in the USPS sandbox before going live.

You need a Consumer Key and Consumer Secret obtained by registering an application on the USPS Developer Portal at developers.usps.com. For label generation and tracking, you also need a valid Customer Registration ID (CRID) and Mailer ID (MID) registered through the USPS Business Customer Gateway. The CRID and MID are separate from the API credentials and are required for OAuth token generation to access the Tracking API and generate labels with an embedded MID in the barcode. If you are migrating from Web Tools, your existing MID should transfer, but the CRID registration may need updating. We walk through this setup with you as part of the integration engagement.

Yes. We build a custom WooCommerce shipping rate plugin that calls the USPS Prices API at checkout and returns live rates based on the buyer's destination ZIP code, the order weight, and the package dimensions you configure. You control which USPS service classes to display (Priority Mail, Ground Advantage, Media Mail, etc.) and can apply markup rules or flat handling fees per service. Rates update in real time as the buyer changes their address. We test the integration against a range of weights, dimensions, and ZIP codes before deployment to confirm accurate rate returns.

The USPS Tracking Webhook pushes scan event updates to your server as they happen rather than requiring your system to repeatedly call the Tracking API to check for status changes. This means your order management system learns about delivery or exception events within seconds of them occurring at USPS, rather than on your polling interval. It also eliminates the API call volume and associated rate limit risk of polling hundreds or thousands of tracking numbers regularly. We build the webhook receiver endpoint on your server, handle USPS signature verification, parse the event payload, and trigger the appropriate actions in your system such as updating order status, sending customer notifications, or flagging exceptions for your operations team.

The USPS Domestic Labels API returns labels in PDF, TIFF, SVG, JPG, ZPL203DPI, and ZPL300DPI formats. PDF is the most universal and works with any printer including standard inkjet and laser printers. ZPL (Zebra Programming Language) is the format used by thermal label printers and produces the sharpest barcode output at scale. If you have thermal printers in your fulfilment operation, use ZPL at the resolution matching your printer's DPI setting (most Zebra printers are 203dpi or 300dpi). We integrate whichever format your print workflow requires, and can build format selection logic if you have a mix of printer types across your fulfilment locations.

Yes. We build multi-carrier rate comparison integrations where USPS rates appear alongside UPS, FedEx, DHL, or other carriers at checkout or in your fulfilment dashboard. The buyer sees a unified list of shipping options and their actual costs, and can choose based on price or speed. For high-volume operations, we can also build intelligent carrier selection logic that automatically routes each order to the lowest-cost carrier meeting the delivery speed requirement, without any manual carrier selection from the fulfilment team. This is particularly effective for businesses shipping a high proportion of packages that qualify for USPS flat rate or Ground Advantage pricing.