In case you're already using a recording solution and would like Loadmill to generate an API Test Suite from it, the following recording methods can be imported to Loadmill :
GoReplay: An open-source network monitoring tool which can record your live traffic, and use it for shadowing, load testing, or detailed analysis and monitoring. You can import Gor files in the recording page by clicking IMPORT RECORDING.
HAR file: Use the browser's Dev Tools to record a HAR file. You can import HAR files in the API and Load Test Editor.
Charles proxy: An HTTP proxy that allows a developer to view all of the HTTP and SSL / HTTPS traffic between their machine and the Internet. Export sessions to HAR files and import them as Loadmill Test Flows.