Disclosed are various embodiments for monitoring network usage by client devices and enforcing compliance rules related thereto. A management component of a client application can be provided to identify a first function call made in the source code of the client application to invoke a media player function on the client device associated with a playback of media content received over a carrier network. The first function call can be replaced with a second function call that, when invoked during an execution of the client application, causes a device to identify a size of the media content received by the client device over the carrier network; communicate the size of the media content received by the client device to a remote computing service; and provide the media content for playback on the client device.