Inside Android Keyboards: Building an Open Source IME

Building an Android keyboard is fundamentally different from building a traditional Android application. Keyboards operate inside a unique part of the Android ecosystem interacting directly with the Input Method Framework (IMF), communicating across applications, handling sensitive user input, and operating under strict performance and lifecycle constraints.

In this session, I will use lessons from maintaining Scribe-Android, an open-source keyboard project, as a practical case study to explore how Android keyboards (IMEs) actually work. We will examine the architecture behind IME, input flows, lifecycle behavior, and the challenges of building software that integrates deeply with the Android system while interacting seamlessly with other applications.

The talk will also cover real-world engineering challenges encountered while building a production keyboard experience: lifecycle quirks, latency and responsiveness tradeoffs, multilingual input support, debugging behavior across fragmented Android devices, and privacy and security considerations unique to keyboard software.

Rather than serving as a project showcase, this talk uses a real-world open-source IME to explore Android system behavior, architectural decisions, and the engineering tradeoffs required to build responsive, privacy-conscious input experiences.

1. Understand how Android keyboards (IMEs) work and integrate with the Input Method Framework
2. Learn core IME architecture: IME input flows, and system interaction
3. Explore engineering tradeoffs around lifecycle behavior, latency, multilingual input, and performance
4. Understand UI tradeoffs between XML and Compose in the Keyboard Layouts
5. Learn debugging strategies for OEM quirks, fragmented Android environments, and platform changes (including API 36 breakages)
6. Understand privacy and security considerations in keyboard software
7. Gain deeper insight into Android internals through building unconventional system-facing software