Sudoku Ultimato

Jan 2026

Sudoku Ultimato started when my dad just wanted to play Sudoku without subscriptions, and I was frustrated with intrusive ads, paywalls, and the lack of variants. I wanted Killer mode, tiny and giant boards, landscape support, and decent stats, so I built it. I had never developed for Android or implemented online leaderboards in a mobile app, so the project became a good opportunity to learn both.

I designed Sudoku Ultimato as a calm and flexible playground for Sudoku players. You can play quick rounds on tiny boards or long sessions on giant grids, switch between Classic and Killer mode, and enable accessibility options like zoom and larger text. Daily puzzles keep regular players engaged, and Killer cages add a deeper logic challenge for people who like to think further ahead.

Main features

Classic & Killer Sudoku
Endless puzzles (generated instantly from seeds)
Daily challenge mode
Multiple board sizes (4×4, 9×9, 16×16)
Light & dark themes
Accessibility options (zoom, text size, haptics)
Landscape support on phones & tablets
Quick input
Minimal ads
Available in English, Dutch, and Thai
Available on App Store and Google Play (soon)

Tech
Built with Flutter, sharing one codebase for iOS and Android. Backed by Firebase for authentication, analytics, leaderboards, and cloud-synced statistics. Each puzzle uses custom Dart logic for generation and solving, with a seed system that tracks puzzle parameters (grid size × variant × difficulty × puzzle number) so players can replay or compare the same puzzle across devices.

The product website is built with Next.js, Tailwind CSS, and deployed as a static export to GitHub Pages with multi-language support.

Flutter
Figma
NextJS
Dart
iOS
Firebase