Sudoku retrospective.

I started building a sudoku game for Android in 2012. It’s been a fun side project over the years, but with no plans to develop it further, it’s time to release the source code and create space for new endeavours.


I’ve been developing Android apps ever since I got my HTC Hero in 2009, but 2012 was when Android development really got exciting. It became a viable career niche. I was working on the mobile apps team at The Guardian, and the Android platform itself was starting to migrate from phones to tablets and other devices.

It was around this time that apps began to feel much more polished. The sci-fi Holo design language marked the beginning of Google getting opinionated on Android UI patterns, and it heralded a wave of flat UIs with neon accent colours. At the time, it was a welcome change from skeuomorphic designs copied wholesale from iOS apps – they never felt quite at home.

Google Play had plenty of sudoku games to offer already, but they were overcomplicated, cluttered with ads, and they often demanded invasive permissions. I started building a minimalist alternative inspired by the simplicity of printed puzzles and the system apps in Android 4.0.

Holo Sudoku featured on Google Play in 2013

It was a huge thrill when the game was featured on Google Play a few months after release. Just a week later, it had been downloaded over a million times. I’d worked on a couple of high profile apps by this point, but it felt incredible to see something I’d made by myself on the front page of the app store.


I returned to this project almost every year, whenever there was a significant evolution of the Android platform. Migrating the codebase from Java to Kotlin was one of the bigger efforts, and that process supercharged my experience with the language. It’s been a handy testbed for putting all sorts of patterns and tools into practice. It kept me moving at the pace of the platform and the Android community.

Screenshots of the last version of the game

Given the initial release leant so heavily on the defaults of the Holo design language, it was natural that the game would later evolve into “Material Sudoku”. Google announced Material Design in 2014 and I jumped right in, redesigning screens to make use of cards, elevation, and bold blocks of colour.


When a side project starts to feel like a chore, it’s time to consider downing tools. I’m no longer excited about building a sudoku game, but I hope somebody will fork the project or learn something from the codebase.