Learn Tsuidoku
Four rules, 81 pairs, two techniques that exist nowhere else. Twenty guides, from your first glance to the diabolic grid.
Get started
6 guidesInteractive tutorial
Five interactive steps on a real grid, from the first rule to your first solve.
Points and ranking
What a cell, a mistake and a hint are worth, and how a ranked game moves your rank.
The 4th Rule of Color Sudoku: The One That Changes Everything
Learn the 4th rule of color sudoku: each color must contain numbers 1–9. See how this single constraint creates 81 unique pairs and unlocks new techniques.
Why Color Sudoku Feels Deeper Than Classic Sudoku
Discover how the color layer interweaves with classic sudoku logic to create richer patterns, more constraints, and entirely new solving paths in Tsuidoku.
Why Try Color Sudoku? 4 Concrete Reasons
Discover 4 clear reasons to try Tsuidoku: more solving tools, 81 unique number-color pairs, exclusive techniques like Rainbow, and a fresh twist on classic sudoku.
Color Sudoku vs Sudoku: What's the Difference?
Compare Tsuidoku and classic Sudoku side by side: 3 vs 4 rules, 9 numbers vs 81 unique pairs, difficulty differences, and exclusive solving techniques.
Color Sudoku: Rules, Types & How They Actually Differ
Color sudoku means two different things: Irodoku (colors replace digits) and Tsuidoku (color as a 4th constraint alongside digits). Here's what separates them.
Color Sudoku Training Plan: From Beginner to Master
A step-by-step training plan to improve at Tsuidoku: what to practice first, when to learn Rainbow and Chromatic techniques, and how to reach master level.
Techniques
3 guides81 Unique Pairs: The Core Rule of Color Sudoku
Why are there 81 combinations in Tsuidoku? Learn the 9 numbers × 9 colors rule, with a clear visual example and how it changes your solving strategy.
Rainbow Technique: Find Missing Colors in Color Sudoku
Use the Rainbow technique to track a number across all 9 colors and spot what's missing. A practical step-by-step color sudoku solving method unique to Tsuidoku.
Chromatic Circle Technique for Color Sudoku
Learn the Chromatic Circle technique to find missing numbers by tracking one color across the entire grid. A clear step-by-step method with visual examples.
By level
7 guidesTsuidoku Difficulty Guide: From Easy to Diabolic
All 6 Tsuidoku difficulty levels explained - Easy (88 clues) to Diabolic (36): what changes, which techniques to use, and how to climb. Free color sudoku.
Easy Color Sudoku (88 Clues): Beginner Strategy Guide
How to play Easy color sudoku (88 clues) on Tsuidoku: read colors as information, master the highlight modes, and build the reflexes every level needs.
Medium Color Sudoku (75 Clues): Strategy Guide
Medium color sudoku (75 clues) on Tsuidoku: crossing two facts, half-clues, and why Medium is the training ground for the worldwide Daily Challenge.
Hard Color Sudoku (62 Clues): Pair-Thinking Strategy Guide
Hard color sudoku (62 clues) on Tsuidoku: the Rainbow Technique, the Chromatic Circle, and how to think in digit-color pairs instead of cells.
Expert Color Sudoku (52 Clues): Notes & Elimination Guide
Expert color sudoku (52 clues) on Tsuidoku: why notes become mandatory, candidate elimination in two dimensions, and cascading digit-color deductions.
Master Color Sudoku (43 Clues): Deep Scanning Guide
Master color sudoku (43 clues) on Tsuidoku: long deduction chains, systematic deep scanning, and the discipline that turns Expert players into Masters.
Diabolic Color Sudoku (36 Clues): The Ultimate Challenge
Diabolic color sudoku (36 clues) on Tsuidoku: the hardest level of the 9-color puzzle. Every technique combined, the 81-pair endgame, and the black-belt mindset.
Understand
4 guides13 Clues Are Enough: Suirodoku Beats Sudoku's 17
Classic Sudoku needs at least 17 clues. Tsuidoku only needs 13 — each clue carries a digit and a color, doubling its information. Here's why.
3.6 Billion Grids: How Many Suirodoku Actually Exist?
We thought there were 9 Tsuidoku grids. There are 3.62 billion — for a single base alone. And 99.92% of candidates don't survive the block constraint.
Solving Suirodoku with Google CP-SAT Solver
How to model Tsuidoku as a constraint satisfaction problem with Google OR-Tools CP-SAT. 243 variables, 136 constraints, one elegant encoding trick.
Suirodoku FAQ: Your Questions About Color Sudoku Answered
Quick answers about Tsuidoku: what is color sudoku, how do the 81 unique pairs work, what are the 4 rules, is it harder than classic sudoku, and how to start.