Complete guide: the three rules of the 9×9 grid, how to reach the digits by elimination, controls on muta.pro — levels, check, hints — and techniques for beginners.
Sudoku is a single-player logic puzzle on a square 9×9 field. The field is divided into nine 3×3 boxes, and some cells are already filled — these are starting clues. Your task is to enter digits into the empty cells so that all three rules are satisfied at once.
There is no math here: nothing needs to be added, only finding the single correct digit for each cell matters. A valid puzzle always has exactly one solution, and you can reach it through pure logic.
Choose a difficulty level — Easy, Medium or Hard. It determines how many cells are revealed at the start: the higher the level, the fewer clues and the longer you have to think.
The revealed digits are fixed — they cannot be changed, they form the framework of the puzzle. All the other cells are empty, and it is up to you to fill them. The timer starts with the beginning of the game, and the counters on the right show how many cells remain and how many mistakes have been made.
In each horizontal row, the digits from 1 to 9 appear exactly once — no repeats.
Each vertical column also contains all nine digits from 1 to 9, and none repeats.
Within each of the nine 3×3 boxes, all digits from 1 to 9 appear once. This is the third and decisive constraint.
For an empty cell, mentally cross out the digits already present in its row, column and box. If only one remains — place it.
Sometimes it works the other way: a digit fits into a row, column or box in only one cell. Then place it there confidently.
Start with areas that have many revealed digits — there the cells are solved fastest and open up approaches to the rest of the grid.
Mini fragments of the 9×9 grid. Revealed starting clues are dark, digits you entered are blue, the found digit is green. The line of reasoning inside a single 3×3 box is shown.
The game is won when all 81 cells are filled and match the correct solution. The grid lights up, and the game shows the result: the time spent and the number of mistakes.
A mistake is a digit that conflicts with one already present in the row, column or box — the error counter then increases. Each hint used also counts. The best times for each level are saved in the record table, so it pays to solve cleanly and quickly.
The bottom panel shows how many copies of each digit have not yet been placed. Pick the one that has almost none left.
A good Sudoku is solved by logic without trial and error. If you feel like guessing, you have missed something — re-read the field.
Highlighting the row, column and box instantly shows the restrictions for a cell — it is a free map of eliminations.
A hint reveals a cell but counts against you. Resort to it only when you are honestly stuck.
Sudoku is solved not by guessing but by a queue of techniques: the cheapest first, and only when they run out — the pricier ones. Such an order saves time and all but rules out mistakes, since every move is strictly forced.
The key idea is not to look for the answer at once, but to narrow the possibilities. Each technique either places a forced digit or removes a superfluous candidate; both bring the board closer to its single solution. Stick to this ladder and even a "hard" level breaks down into a series of obvious steps.
Take one digit, say 9, and run it across all the boxes. Often it is forced into the only free cell of a box — that opens the board up fastest.
Look at a cell: if its row, column and box together exclude eight digits, the ninth must stand right here. The main move on the easy level.
Look at a line or box: if a digit fits there in only one cell, place it there, even if other candidates formally remained in the cell itself.
When the obvious moves run dry, write all possible candidates into the cells. Only through them do the pairs, triples and pointing pairs of the next level become visible.
Naked single: the box's eight digits rule out everything except 4 — the central cell is forced.
At the medium and hard level the singles run out, and techniques come into play that don't place a digit but strike out candidates. Each such elimination sooner or later gives rise to a new single — that is the whole strength of the method.
These techniques work only on written-out candidates, so first carefully fill in the marks in the stuck zone. Then look for where two or three cells share the same digits: such links are what let you remove a candidate outside the link.
Naked pair {3,7}: two cells share exactly these two digits, so 3 and 7 can be struck out of the other cells of the box and row — the cell with "?" clears up.
Two cells of a line with the same two candidates {a,b} take both digits between them. Strike a and b out of all other cells of that line.
If in a box a digit is possible only in the cells of one row or column, along that line beyond the box you can safely erase it.
If two digits within a line occur only in the same two cells, all other candidates are removed from those cells — the pair "undresses."
Pointing pair: in the box the digit 2 is possible only in the top row — so in that row outside the box we strike the two out.
On muta.pro the three levels differ in the number of given cells and the depth of the techniques needed. The higher the level, the longer the chain of eliminations before the first new digit.
Plenty of clues; scanning and naked singles suffice. Marks are hardly needed — the board opens up by a straight look-through.
Singles run out fast. Without pencil marks and naked pairs you can't move on — here the technique from the second section becomes mandatory.
Pointing pairs, hidden pairs and sometimes X-Wing come into play. Bet on the order of techniques: cheap scans first, expensive chains after.
Classic sudoku is a 9×9 grid with 3×3 boxes, and it is exactly this one you solve on muta.pro. Beyond it exist dozens of kindred puzzles with the same logic of "each digit once."
To the three rules both main diagonals are added: on each, too, all digits 1–9 without repetition. The diagonals give extra eliminations.
Reduced grids with digits 1–4 or 1–6. The same rules, but shorter — handy for practicing scanning and singles.
Almost all sticking points in sudoku come not from the difficulty of the task but from broken discipline: guessing, forgotten marks, haste. Remove them — and the "hard" level stops seeming unmanageable.
A useful self-check rule: before every digit ask yourself why it is forced. If there is no clear answer — this is not a move but a guess, and it is better set aside, returning to scanning and marks.