Facebook routinely tracks users, non-users and logged-out users outside its platform through Facebook Business Tools. App developers share data with Facebook through the Facebook Software Development Kit (SDK), a set of software development tools that help developers build apps for a specific operating system. Using the free and open source software tool called "mitmproxy", an interactive HTTPS proxy, Privacy International has analyzed the data that 34 apps on Android, each with an install base from 10 to 500 million, transmit to Facebook through the Facebook SDK.