There are many great developer tools for working with REST APIs. Even better, most of them are free and open source. Here are a few that we really like here at ShipEngine:
Another free, open source , command-line tool. Whereas curl is ideal for scripting, HTTPie is optimized for interactive use. It has a very user-friendly UI, colorized and formatted output, and other features that make it really nice to use.
A free, cross-platform app that makes it easy to experiment with APIs in a friendly interface. You can get started quickly by downloading one the official ShipEngine Postman collections.
Another free, open source, cross-platform app that lets you experiment with APIs in a nice visual interface.
Many developer tools allow you to import API definitions and automatically generator wrapper classes, SDKs, mock servers, contact tests, etc. Here are API definitions for ShipEngine in a few of the most widely-supported formats:
OpenAPI 3.0 (formerly known as Swagger) is the most popular format for REST API definitions. It's supported by a wide variety of tools.
These are full JSON Schemas for every request and response in ShipEngine. You can use these schemas with any of countless JSON Schema tools to perform validation, generate models, etc.