Postman

Postman is a testing tool for developing APIs. I have a small amount of experience with this one, but came to love it very quickly while creating requests to send to an API I've been working on. The UI is intuitive, clean, and easy to use.

From the request page, you're offered a selection of HTTP services, such as "Get," "Post," "Put," Delete," and more. You're able to select the Parameters ("Params"), Authorization, Headers, Body, Pre-Request Script, Tests, and Settings tabs to further configure your test request. 

My favorite feature to date is in the Body tab. You can add an existing form to send, x-www-form-urlencoded, Raw, Binary, or GraphQL. When you select one of these types, such as Raw, a type box appears below and a drop down menu that allows you to select your type of text (text, javascript, json, html, or xml). Cool, right?! At the bottom of the application is a window with the returned response from the tested API, which can also be configured! You can choose to have the format of the response to be configured to "Pretty," an easy to read format, Raw, Preview, Visualize, and a specific text type, just like when you configure a request (json, xml, html, text, and auto setttings).

This is an image from the API I was adding services to:

You can see the features I mentioned in the image.

There are many other features on this tool, such as creating a new collection, environment, documentation, mock server, monitor, and API. Without experience, I don't have anything to add about these features in the moment, but I'll add information when I do!