Advanced Rest Client, Postman-Rest Client, and Curl in Linux are some REST API testing tools that developers may use to see if a REST API is completely ready to use. Follow these steps. In the tool’s textbox, type in the API’s URL. Choose an HTTP method for this API (GET, POST, PATCH, etc.). In the Headers textbox, type any headers that are necessary. Use a key-value pair to pass the API’s request body. Select the appropriate content type (such as application or JSON). Send your message. After hitting Send, the REST API will respond with various replies, indicating whether the API testing was successful or unsuccessful. It’s crucial to keep track of the response code, message, and body.