USPS offers public APIs known as the USPS Web Tools, or USPS Web Tools API, for some key services. These APIs just offer access to Tracking, Address Verification, and Rates.
One crucial area that's lacking from the USPS Web Tools is the ability to purchase postage or shipping. All this has been delegated to USPS partners such as EasyPost. EasyPost is a and offers all USPS Web Tools functionality and more.
With the EasyPost API, you get the best of USPS Web Tools and the best of purchasing capabilities (postage, refunds, scan forms, batches, etc.) all in one RESTful JSON API with client libraries in PHP, Java, Ruby, Node, .Net, Perl, Python, and more.
EasyPost offers the following USPS API services:
The EasyPost API offers the following USPS service levels: