The three rules, the grid sizes and difficulty levels, a worked example on a real board, every button on the game, and a practice puzzle you can play right here.
Mini Sudoku is classic Sudoku on a smaller grid. The version most people meet first is the 6×6 board that LinkedIn features among its daily games: 36 cells, the digits 1 to 6, and six boxes that are two rows tall and three columns wide. There is no arithmetic anywhere in it. The digits are just six different symbols, and the whole puzzle is about where each one can and cannot go.
This site has that 6×6 plus two bigger sizes, 8×8 and 10×10, all with the same rules. For the background (where Sudoku came from and how the mini compares with classic and killer Sudoku) read What is Mini Sudoku?. This page is the practical part: the rules, one full worked example, a board to practise on, and what every button does.
The Three Rules
A puzzle starts with some cells already filled in. These are the clues, also called givens, and they are shown in grey. You cannot change them. Your job is to fill every empty cell so that:
Every row contains each digit exactly once. On a 6×6 that means 1, 2, 3, 4, 5 and 6, once each, across the six cells of the row.
Every column contains each digit exactly once.
Every box contains each digit exactly once. The boxes are outlined with thicker lines. On a 6×6 they are 2×3 rectangles, so there are six of them: three stacked down the board, two across.
3
1
5
2
6
4
4
1
6
5
2
4
5
6
2
3
A finished row: 1 to 6 once each. Every row and every column works the same way.
2
5
1
3
4
3
6
2
1
4
3
5
2
A finished box: the top-left 2×3 rectangle also holds 1 to 6 once each.
That is the whole rulebook. Each row, column and box has exactly as many cells as there are digits, so “no repeats” also means “nothing missing”. Every puzzle on this site has exactly one solution (all 1,740 in the library have been checked with a solver), so if you ever find yourself choosing between two digits by feel, there is a deduction you have not spotted yet.
Why rectangles? A 9×9 grid splits neatly into 3×3 squares because 9 is a perfect square. Six is not, so the 6×6 uses boxes of two rows by three columns: six boxes of six cells, which is exactly what the rules need. The 8×8 uses 2×4 boxes and the 10×10 uses 2×5. The shape changes how you scan (a 6×6 box lines up with the box beside it along two rows, and with the boxes above and below it along three columns), but the rules never change.
Grid Sizes and Difficulty
There are three grid sizes and four difficulty levels. The daily puzzle is always a 6×6, medium early in the week and hard at the weekend; the bigger grids live in the puzzle library.
Difficulty is graded by the logic a puzzle needs, not only by how many clues it has. A solver works every board the way a person scans, always taking the easiest move available, and each level has a ceiling its boards never go past:
Easy boards fall to box scanning alone: pick a digit, and there is always a box where it fits in only one cell. A 6×6 easy board starts with 16 to 18 clues. Easy boards are for Unlimited and the library; the daily is never easy.
Medium boards are still solved by scanning, with fewer clues (12 to 14 on a 6×6). Now and then a digit's only home is easier to see in a row or column than in a box.
Hard boards have about the fewest clues scanning can still finish, 10 to 12 on a 6×6. You never need pencil marks, but the next move is harder to find, and some boards need a row or column scan to get going again.
Expert boards are where scanning runs out. You will need pencil marks and the elimination techniques on the techniques page to get past the sticking points.
For practice, Unlimited serves 6×6 boards one after another with an easy, medium, hard or expert filter, and the library pages sort every board by size and by difficulty.
A Worked Example
Here is a real 6×6 board that starts with 13 clues. We will place the first six digits and name the technique behind each one. Nothing is guessed, and every technique links to its longer explanation on the techniques page. Rows are numbered from the top and columns from the left.
The starting position
6
5
3
5
1
1
2
5
4
5
6
1
4
13 clues. Three cells can already be settled from the clues alone; the trick is finding them.
Step 1
6
5
3
5
1
1
4
2
5
4
5
6
1
4
Row 4, column 3 and the middle-left region rule out 1, 2, 3, 5 and 6. Only 4 is left.
Step 1 · Naked single
Start where a cell has almost nothing left. Look at row 4, column 3. Its row already holds 1, 2 and 5. Its column holds 3, 5 and 6. Its box, the middle-left one, holds 5 and 1. Put those together and 1, 2, 3, 5 and 6 are all taken, so the cell can only be a 4. A cell with a single candidate left is called a naked single, and it is always the first thing to look for.
The 1s in columns 4 and 6 sweep the top-right region. One cell survives.
Step 2 · Cross-hatching
Now pick one digit and follow it around the board. There are three 1s among the clues. The top-right box has none yet. The 1 in column 6 rules out both of that column's cells in the box, the 1 in column 4 rules out both of its cells, and row 1, column 5 is already a 5. The only cell left is row 2, column 5, so the 1 goes there. Sweeping a digit's lines across a box to see which cell survives is called cross-hatching.
The 1s in row 6 and column 2 sweep the bottom-left region.
Step 3 · Cross-hatching
Stay with the 1s. The bottom-left box needs one too. The 1 in row 6 rules out the two open cells on the box's bottom row, the 1 in column 2 rules out the cell above them, and the 4 and the 6 are clues. That leaves row 5, column 3.
The two 1s you just placed sweep the top-left region. The last 1 goes in the corner.
Step 4 · Cross-hatching
The two 1s you just placed now do the same job for the top-left box. The 1 in row 2 rules out both open cells on the box's second row, and the 1 in column 3 rules out row 1, column 3. The 6 and the 3 are clues, so the 1 goes in the top-left corner. All six 1s are now on the board, three of them found by following a single digit. Your own placements are clues too.
Column 3 now holds 3, 5, 4, 1 and 6. Its one empty cell must be 2.
Step 5 · Last cell in a column
Look down column 3: the rows below the top now read 3, 5, 4, 1 and 6. The only empty cell is at the top, and the only digit the column is missing is 2. A cell that is the last gap in its row, column or box is the easiest single of all. You do not even need to check the other two groups; just ask what is missing.
Row 3 needs a 4. Three of its four empty cells are blocked, so the 4 goes here.
Step 6 · Hidden single
Row 3 reads blank, blank, 5, blank, blank, 1, so it still needs 2, 3, 4 and 6. Ask where its 4 can go. Column 1 already has a 4 (in row 5), which rules out the first cell. The second cell sits in the middle-left box, which got its 4 in step 1. Column 5 has a 4 in row 6, which rules out the fifth cell. Only the fourth cell is left, so row 3, column 4 is a 4, even though that cell on its own could still hold a 3, 4 or 6. A digit with only one home in a row, column or box is a hidden single.
Six digits in, and the board has opened up. From here it finishes with naked and hidden singles alone, the same two ideas over and over, with no pencil marks needed. Notice how each step fed the next: the 4 from step 1 was the reason step 6 worked, and the 1s placed in steps 2 and 3 were what cracked the top-left box.
An easy 6×6 from the library: every cell on it can be found by picking a digit and looking for the one place it fits in a box. Press Play to start the timer, tap a cell, then tap a number. If a digit turns red, it is wrong. When you solve it, Next puzzle in the results card gives you another easy board from the same set. Solves here are kept apart from your daily streak and your unlimited best times.
Mini Sudoku 6x6 #0007
easy • 6×6
00:00
Hints 3
63
Mini Sudoku
The Board and Its Tools
Every board on the site has the same controls: the grid, a row of three buttons (Notes, Clear, Undo), the number pad, and a bottom row with Hint and Reset. Here is what each one does.
Selecting a cell
Tap or click a cell to select it. It gets a green outline, and its row, column and box are shaded, so you can see every cell it has to agree with. If the selected cell holds a digit, every other copy of that digit on the board turns bold, which makes it quick to check where a digit already sits before you cross-hatch it.
Placing digits
With a cell selected, tap a digit on the number pad (or type it). Tapping a different digit replaces the one in the cell. When every copy of a digit is correctly placed, its button on the pad fades and is crossed out, a small signal that you can stop looking for it.
Notes (pencil marks)
Tap Notes to switch the pad into pencil-mark mode. Each digit you tap is now added to, or removed from, the selected cell as a small candidate mark. Tap Notes again to go back to placing full digits. Placing a digit clears that cell's marks, but marks elsewhere are left alone, so keep them up to date yourself. Notes earn their keep on medium and hard boards, where hidden singles and pairs only show up once candidates are written in.
Clear and Undo
Clear empties the selected cell, removing its digit and its marks. Undo steps back through your own moves one at a time (placed digits, cleared cells and pencil marks) and remembers up to the last 200 of them. Ctrl+Z, or Cmd+Z on a Mac, does the same. Hints are not undoable, and once a puzzle is solved the board is locked.
Hint
You get three hints per puzzle, shown in the badge above the board. Press Hint and it marks a cell you can solve next with a dashed outline and says why under the buttons, for example “4 is the only digit missing from row 2”. Press Hint again, or Fill it, to place the digit. If the cell you have selected can be solved, Hint explains that one, and if a digit on the board is wrong, Hint points there first. A hint is used when it points at a new cell; filling that cell is free. The timer keeps running while you use hints.
Mistakes
The board checks every digit against the solution as soon as you place it. A wrong digit turns red, and so does any digit it repeats in the same row, column or box. There is no mistake limit and no time penalty: clear it, type over it, or press Undo.
Reset, New Puzzle and difficulty
Reset puts the board back to its clues, sets the timer to zero and gives you your three hints back. On the homepage, on Unlimited and on the library puzzle pages, New Puzzle loads another board of the same size, and the All, Easy, Medium, Hard and Expert buttons above the grid choose which difficulty it comes from.
Timer and results
The timer starts when the board loads (on the homepage, when you press Play) and stops the moment the last correct digit goes in. The results card then shows your time, your best time for that grid size, and either your streak (for the daily) or how many puzzles you have solved this session, with a chart of your solving pace. Share copies a one-line result with your time, or opens the share sheet on a phone.
Keyboard and Touch Controls
On a phone or tablet, tap a cell and then tap a number; that is all you need. Tapping anywhere outside the board and its buttons clears the selection. On a computer, click a cell once and the keyboard takes over:
Keyboard shortcuts
Key
What it does
1–9
Place that digit in the selected cell, or toggle it as a pencil mark when Notes is on. On a 10×10, enter 10 from the number pad.
←↑→↓
Move the selection one cell. It stops at the edge of the board.
BackspaceDelete
Clear the selected cell: its digit and its pencil marks.
Ctrl+Z
Undo your last move (Cmd + Z on a Mac).
Tab
Move focus through the cells and buttons. Enter or Space selects the focused cell.
Digit keys only go up to the board's size, so a 7 does nothing on a 6×6. The keys act on the selected cell, and they are ignored while you are typing in a text box such as the feedback form.
Daily Puzzle, Streak and Best Times
There is one daily 6×6 each day, and everyone gets the same board. On the homepage it sits behind a Play card, so the timer does not start until you are ready. Solve it and your streak goes up by one; solve the next day's and it keeps growing; miss a day and it starts again. Days are counted on US Eastern time, and only the daily board counts.
Your streak and your best time for each grid size are saved in your browser, with no account or sign-up. Daily best times are kept separately from everything else. A puzzle in progress is not saved, so if you reload the page the board starts over. Clearing your browser data, or moving to another device, starts your streak and best times fresh.
Common Mistakes to Avoid
Checking one group instead of three. A digit can look fine in its row and still clash with its box. Before you place anything, run your eye along the row, down the column and around the box. The shading on the board shows you exactly which cells those are.
Guessing when you stall. Every board has one solution that logic reaches, so a guess only hides the real deduction. When nothing is obvious, pick a digit and cross-hatch it through every box, then look for a row or column where a digit has one home left.
Letting pencil marks go stale. The board does not tidy your notes for you. Each time you place a digit, remove it from the marks in the same row, column and box, or the marks will start lying to you.
Starting with the emptiest part of the board. The busiest row, column or box is where the rules have already done most of the work. Start there, and let each placement feed the next one.