The on-device web interface is built using ReactJS, Charts.js & Canvas Gauges and simply invokes REST APIs made exposed by the firmware.
Customisable Web Interface
As the packaged ReactJS app is served from a dedicated partition by the C++ core, it can be replaced entirely with any application written in JavaScript that calls these REST APIs.
REST API
The APIs themselves are documented here. They can also be used centralised automated control of AirMeter.io devices.