The Selenium and Appium projects are both platforms which allow for programmatic simulation of user interaction on Browsers and Mobile devices respectively, for testing purposes.

Part of the success of these projects is due to their choice of handling commands as HTTP API. This allows for QA professionals to use the testing framework and language of their choice.

I will discuss the internals of the Webdriver API, the JSON Wire protocol, and the current draft of the Mobile JSON Wire protocol, an extension under development for testng on Mobile Devices.

Sauce Labs offers an API built on top of these protocols, allowing one to shift from running tests locally, to running tests across a range of devices on multiple machines in parallel.