A Strategy Guide to Rush Sudoku

Rush Sudoku is one of the games we built ourselves, so unlike everything else on this site we can tell you exactly how it works underneath. This guide covers the tools on screen, the structure of the board, and the order in which techniques are worth applying.

The rules are the ones you already know. Fill the nine-by-nine grid so every row, every column and every three-by-three box contains the digits one to nine exactly once.

What is on the screen

The grid sits on the left. Given digits are shaded and cannot be edited; everything else is yours. Tap a cell to select it, then pick a digit from the pad. Tapping the same digit again removes it, which is faster than reaching for the eraser when you immediately change your mind.

Notes toggles pencil-mark mode. With it on, a digit goes into the cell as a small candidate mark laid out in its own position within a three-by-three arrangement, so a candidate 7 always sits in the same corner of every cell. That consistency is the whole point — after a few minutes you stop reading the marks and start recognising their shapes.

Clear empties the selected cell, notes and all. Placing a real digit in a cell clears that cell’s notes automatically, which is the behaviour you want and occasionally the behaviour that catches you out if you were using notes as a scratchpad.

Check marks every wrong entry and reports how many there are. Note what it does not do: it will not tell you which cells are wrong until you press it, and it will not hint at what belongs there. It is a debugging tool for a grid that has gone bad, not a substitute for the deduction.

Underneath, a small line reports a unique solution check on the board you were dealt. Every daily grid is verified to have exactly one solution, which matters more than it sounds — it is the guarantee that lets you treat “there is only one digit that fits here” as a valid argument rather than a hopeful one.

There is a Daily board that is the same for everyone on a given day, and a Practice button that deals a fresh grid whenever you want one.

How the board is generated

Here is the part nobody else can tell you about their sudoku.

Every board comes from a single underlying grid. To make the day’s puzzle, the generator shuffles the three horizontal bands of rows and the rows within each band, does the same to the vertical stacks of columns, and then relabels all nine digits according to a shuffled mapping. Each of those operations preserves sudoku validity, which is why the result is always a legal grid with exactly one solution.

The practical consequence is worth understanding. The pattern of given digits is a permutation of one skeleton, so the shape of the deduction is stable from day to day even though the positions and the digits move. Boards carry thirty givens. If today’s grid felt like it opened in the middle-left box, tomorrow’s will open somewhere that corresponds to it, transformed. Regular players start recognising the rhythm of the solve rather than the specific numbers, and that recognition is a legitimate skill the game rewards.

If you want boards that vary more in feel, the practice button is the answer — it seeds from the moment you press it rather than from the date.

The order to work in

Scan the crowded digits first. Count which digit already appears most often on the board and place the rest of its copies. Six or seven placed nines usually force the remaining ones outright, and every placement narrows other digits for free. This alone finishes an easier grid.

Scan boxes, not just lines. The commonest beginner habit is reading along rows and columns and missing eliminations that only appear within a three-by-three block. If two cells of a box are excluded by a row and a third by a column, the digit is placed — and you never see it looking at the lines alone.

Only then reach for notes. Filling every candidate into every empty cell is a lot of work and mostly wasted. Do it one region at a time, on the box or column that is nearly full, because that is where the useful patterns are. Two cells in a box holding the same pair of candidates and nothing else means neither digit can go anywhere else in that box, and that is usually the deduction that unlocks a stuck grid.

Stop guessing on a hard board. One wrong entry propagates, and you will spend longer unpicking it than you saved. If nothing is forced, go back to the crowded-digit scan on a different digit rather than committing to a maybe.

Using Check well

The temptation is to press it every few entries as reassurance. That turns the puzzle into a game of trial and error and removes the only interesting part.

The better habit is to solve until you are genuinely stuck or genuinely finished, and press Check once. If it reports zero, the grid is sound and your reasoning holds. If it reports three, you have a contradiction somewhere upstream, and the marked cells tell you where the chain went wrong — which is far more instructive than being told the answer.

Where to go next

If you want the same kind of thinking in a different shape, Glow Grid and Pixel Trace are the two other logic boards we make, and the catalogue version of Sudoku is worth a look for its difficulty settings. The rest of the shelf is in the puzzle collection.