Join Sudoku — rated sudoku, against someone

What makes it different

Three things no other sudoku app does

Most sudoku apps are a grid and a timer. This one has an opponent, a rating that means something, and a coach that knows why you're stuck.

It knows why you're stuck

Not a hint that hands you a digit. It finds the technique the position actually needs — a hidden single, a pointing pair, an X-Wing — names it, and shows you where to look. The number stays yours to work out.

Difficulty means something

Not clue count. Every puzzle is solved with a capped set of techniques to find which one it genuinely requires. 43% of minimal grids fall to simple singles — so clue count was always a lie.

A rating you can't farm

Every level and every time control keeps its own rating, the way chess separates blitz from rapid. An easy grid can never inflate a hard one.

Variants

Puzzles a solver can't touch

Thermometers, German whispers and killer cages add rules the grid has to obey. They make for better puzzles — and they happen to be the strongest anti-cheat measure in the game, because a public sudoku solver simply cannot read them.

solution, once the constraints are understood. Every variant puzzle is generated to be exactly as unique as a classic one.

500+

solutions to an off-the-shelf solver. Paste a variant grid into any public tool and it hands back garbage — the constraints are invisible to it.

Thermometers

Digits climb from the bulb to the tip. Never equal, never backwards.

German whispers

Neighbours along the line differ by at least five — which means a 5 can never sit on one.

Killer cages

Each dashed cage holds distinct digits adding to its corner number.

There is a second payoff. Extra rules carry information, so far more clues can be removed: a classic grid bottoms out near 25 givens, a mixed variant grid at 17.

Practice

Drills that put the technique in front of you

Six techniques, from naked singles up to X-Wings. Each drill drops you into a real position where that technique is the next step — nothing easier will crack it — then walks you through it in three parts: where to look, why it works, what it gives you.

Step 1

Where to look

The unit lights up. Nothing else is given away.

Step 2

Why it works

The cells that prove it are marked, with the reasoning in plain words.

Step 3

What it gives you

The placement, or the candidates it lets you strike out.

And when a race stalls, Stuck? names the technique you're missing and offers the lesson for it — your clock pauses while you learn, and the race is waiting when you come back.

Ways to play

Four of them, all rated

Race

First correct solve

Five levels, graded by the technique they demand. The purest version.

Clocked

Bullet, blitz, rapid

One to thirty minutes. Most correct squares at the buzzer — filling them is easy, being right is not.

Variants

Thermo, whispers, cages

Extra rules, fewer givens, its own rating.

Challenge

Send a friend a link

They get your exact grid and race your recorded solve, move for move. No account, no server — the whole race rides in the URL.

The ladder

Five levels, graded by the technique they demand

Each one is generated by digging clues out until the puzzle needs exactly the right kind of reasoning — and no less.

GentleNaked and hidden singles, and plenty of clues

EasyStill only singles — but dug as deep as they go

MediumPointing pairs and box-line reduction

HardNaked pairs and X-Wings

BrutalWhatever survives. Chains, and no promises

Sudoku, but someone's
catching up.