Rules
Fill each row, each column, and each region with the digits once. Thick walls split the grid. Two cells that share a side can sit in different regions, and a region can reach far from where it starts.
- One of each digit. Every row, every column, and every region holds each digit once. A 4×4 uses 1 to 4, a 6×6 uses 1 to 6, an 8×8 uses 1 to 8, and a 9×9 uses 1 to 9.
- Thick walls. There are as many regions as the grid is wide. Each region has that many cells, joined edge to edge. The shapes change from puzzle to puzzle, and most of them are not rectangles.
- Givens. Some cells start filled. Those digits are bold, sit on shaded tiles, and cannot be changed.
- Finished. The grid is done when every cell is filled and no row, column, or region repeats a digit.
The outlined region bends: one cell on the top row, then three cells in the row below. The other three regions bend too. None of them is a rectangle. Givens stay bold. Walls, frame, and the digits you placed turn teal.
- Region
- Given
- Your digit
- Pencil notes
Sudoku is one digit per row and per column. The boxes there are regions here. A house is a row, a column, or a region.
Tap a cell. Its row, column, and region are tinted, and the region is outlined in violet. Any other cell with the same digit is a little darker. Type a digit or use the keypad. Erase, Backspace, Delete, or 0 clears it. Arrow keys move. Notes (the Notes button, or N) are pencil marks. Shift with a digit toggles one note without turning Notes on. The board will not fill the notes in for you.
When you place a digit, that digit leaves the notes in the rest of its row, column, and region, in the same undo step. The line under the keypad reads “Row 2, column 3 · 11 cells to go”, or “Given 4 · 1 of 4 on the board”, or “Placed 3 · 1 of 4 on the board”. Solved, it reads “Every row, column and region has each digit once.” The small number on a keypad key counts how many of that digit are still to place. A digit that is already on the board enough times is dimmed.
A row, a column, or a region that holds each digit once turns soft teal while you are still solving. The whole board, walls included, turns teal when it is solved. Givens stay bold ink.
Singles
Write a cell with one digit left, the last empty cell of a row, a column, or a region, and a digit with only one home.
Only one digit left
Look at an empty cell and cross off every digit already in its row, its column, and its region. If one digit is left, write it. This is the usual first press on a 4×4. Most larger easy grids open in the only-home section.
The toast says the row, the column, and the region have already used every other digit. That is stronger than the rule. Name the houses that actually hold a digit. If a house is empty, it did not help. See naked singles.
Row 1 already holds 2 and 4. The region already holds 1, on the shaded given in the row below. The digits 1 to 4 leave 3. Column 4 is empty, so the row and the region did this. The new 3 takes the ring.
When your notes on a cell are a single digit, and the houses still allow more than one, Hint uses the note sentence instead. Notes are manual. See pencil marks.
The houses still allow 1, 2, 3, and 4. Row 6 already has 5, and column 6 already has 6. The region has not removed 1, 2, or 4. The note is only 3, so the cell is 3. “Your notes leave only 3 for this cell, so it is 3.” This is not the first press on a blank grid. The note is what makes it the hint.
After the 3 on the 4×4, the next press is a full house. That is the next section. A later cell on the same board also has one digit left. It is the same sentence, so it is not drawn again.
The last empty cell
When a row, a column, or a region has one empty cell, that cell takes the missing digit. Hint checks this before “only one digit left”, so the toast is the house sentence even when the cell could also have been a single. On the blank 4×4 no house is one cell short, which is why the previous section came first. See full houses.
Row 1 holds 2, 4, and the 3 just written. The empty cell takes 1. “Row 1 has one empty cell left, so it takes the missing 1.” The region beside it still has an empty cell, so this is the row, not the region. The 3 stays violet. Givens stay bold.
The washed region holds 1, 2, and 4, so the empty cell is 3. The cell could also have been “one digit left”. Hint checks the last empty cell first, so the sentence is the region. “This region has one empty cell left, so it takes the missing 3.” Row 2 still has more than one empty cell, and so does column 1.
Column 3 holds 4, 2, and 1, so the empty cell is 3. “Column 3 has one empty cell left, so it takes the missing 3.” The same sentence, with the line named. Two presses between this and the region wrote a 2, then the last cell of row 2. Same ideas, so they are not drawn again.
The only home
A digit can be forced when the cell still has several candidates. The row, the column, or the region has only one cell left that can hold it. On this site that is an easy step. On the Sudoku guide it is a medium step. See hidden singles.
A 4×4 usually does not open here. Larger easy grids often do. The daily puzzle is a 9×9 easy grid, and the first press there is often this one. The column figure is a 6×6 easy grid’s first press. The region figure is the next press on that same grid.
3 can only go in the ringed cell of column 1. The cell can still be 2, 3, 4, or 6, so this is not “one digit left”. The other cells of the column see a 3 already: two of them share a region with the given 3, one shares a region with the other given 3, and one shares that given’s row. The bottom cell is the given 5. “3 can only go here in column 1.” The last column is a straight strip, a rectangle. This hint is about column 1. The ringed cell sits in a bent region.
The washed region bends along the bottom. 3 has one home in it, and that cell can still be 2, 3, or 4. The other cells see a 3: the new 3 in column 1, the given 3 above, or the given 3 in the same row. “3 can only go here in this region.”
The same region sentence shows up on the 4×4 once row 2 is full. 1 has one home in the bottom-left region. That 1 is already written on the column figure above, so it is not drawn a second time.
An easy grid finishes with these singles. A last empty cell, a cell with one digit left, and a digit with one home. A medium grid is where a region and a line have to be read together.
Region and line
If a digit inside one region can only sit in one row or column, it leaves the rest of that line. Read a line the other way when its digit can only sit in one region.
Pointing
If a digit inside one region can only sit in one row, it cannot sit anywhere else in that row. The same is true of a column. You need two or more cells of the region on that line, and at least one cell outside the region that still allows the digit. Hint strikes every such cell in one press.
This is a medium step here. The Sudoku guide lists it under hard, inside a box. See pointing. A row and a column use the same toast with the line name swapped. Both figures are one 6×6 medium grid. Pointing shows up on the medium grids and the hard grids here. An easy grid finishes before it.
The bottom-left region is a 3×2 rectangle. A given 4 blocks every cell of that region in column 1, so the homes left for 4 are the three cells in column 2. Outside the region, only the ringed cell still allows 4. “In this region, 4 can only be in column 2, so 4 is removed from the rest of column 2.” The press strikes that one cell. A rectangle is still a legal region. Most regions are not rectangles.
The washed region is not a rectangle. A given 5 blocks every cell of its bottom row, so the region’s homes for 5 are two cells in row 5. The two ringed cells are outside the region and still allow 5. “In this region, 5 can only be in row 5, so 5 is removed from the rest of row 5.” Both cells lose 5. The two cells at the left of the row already see that given 5, so they are left alone.
Claiming
Read the line the other way. If a digit in a row, or in a column, can only sit inside one region, it cannot sit anywhere else in that region. You need two or more cells on the line, and at least one cell of the region off that line that still allows the digit. One press can strike several cells. See claiming. On the Sudoku guide this is a hard step. Here it is medium.
A 6×6 medium grid finishes with pointing. Claiming shows up on an 8×8 or a 9×9, and not on every one of those grids. The figure is an 8×8 hard grid because that is a state where every pencil mark still holds the real digit. The sentence is the same one a medium grid uses.
In column 1, the only cells that can still be 2 sit in one region. The rest of that region loses 2 where it still has 2, which is the two ringed cells. “In column 1, 2 can only be in one region, so 2 is removed from the rest of that region.” The small notes elsewhere keep an earlier step from firing. They are not the lesson.
The next press on this board claims along a row and strikes one cell. The column already teaches the rule.
Medium adds pointing, and on an 8×8 or a 9×9 it adds claiming. A 6×6 medium grid stops at pointing. Hard is where two cells share two digits.
Pairs and triples
Two cells that share two digits, two digits that share two cells, and three cells that share three digits.
Two cells, the same two digits
If two cells in a row, a column, or a region can only be the same two digits, those digits belong to them and come off every other cell of that house. See naked pairs. The examples here are rows and columns. The rule still applies to a region.
The toast says both digits are removed from the rest of the house. The move edits only the cells that still have them. Some hard grids never show a pair. Pointing and claiming already ran. The pair is the extra step on the grids that still stall, not the step that makes every hard grid hard.
The two washed cells in column 6 can only be 4 and 7. One of them is down to those digits because a note already dropped a 3. The other has no note, and 4 and 7 are what the column still allows. “These two cells can only be 4 and 7, so 4 and 7 are removed from the rest of column 6.” The press strikes 4 and 7 on the two ringed cells, and on no other cell.
Two digits, only two cells
Look from the digits instead of from the cells. If two digits in a row, a column, or a region have only two homes, and those homes are the same two cells, every other note in those cells can go. This is the hidden pair inside the pair section of the Sudoku guide. The examples here are rows and columns. The rule still applies to a region.
The toast says the other notes in them are removed. The returned move may edit only one of the two cells, and only one digit, because the other extras were already gone. Name the cell and the digit the move actually strikes.
In row 2, 4 and 6 can only go in the two washed cells. One of them is already only 4 and 6. The other still has an 8. “In row 2, 4 and 6 can only go in these two cells, so the other notes in them are removed.” The sentence talks about both cells. This press removes 8 from the ringed cell and nothing else. The notes outside the row keep an earlier step from firing. The whole grid stays, because those walls are why the candidates look like this.
Three cells
Three cells in a house that can only be the same three digits take those digits off the rest of the house. See naked triples. A triple is rare. Do not expect one on every hard grid.
The how-to also names a hidden triple: three digits with only three homes. That sentence is in the solver. The grids here finish without asking for one. The Sudoku guide describes it in the same triple section.
The three washed cells in row 4 can only be 2, 3, and 7 between them. “These three cells can only be 2, 3 and 7, so 2, 3 and 7 are removed from the rest of row 4.” The toast names three digits. This press removes 3 from the ringed cell, because 2 and 7 were not penciled there. No other cell of the row is edited.
Hard adds pairs and, on some grids, a triple. Nothing in the ladder asks you to guess.
What if
There is no trial step. You do not write a digit to see whether the grid breaks, and Hint will not ask you to. If a digit is wrong and it does not repeat in a row, a column, or a region, nothing turns red.
The 3 in the first cell repeats nothing. Row 1 has 2 and 4, column 1 is otherwise empty, and the region has 2 and 4. The digit stays violet. Check says “No mistakes so far. Keep going!” Hint has nothing to say, and it does not erase the 3. Erase it and go back to the singles.
A pencil mark that hides the real digit does not by itself make Hint go quiet. Hint may fill a different cell that is still forced. The picture that matches a refusal is the placed 3, not a bad note. The red figures in the next section are the failures Check does catch.
Common mistakes
Check turns a cell red when a digit repeats in a row, a column, or a region. Empty cells on an unfinished grid are incomplete, not wrong. Notes are not errors. The quiet 3 in the previous section is the miss Check does not catch.
Two 3s in row 3, in different regions and different columns. The repeat is the row. Check cites those two cells.
Two 3s in column 1, in different rows and different regions. One of them happens to be the digit that belongs there. Check flags both cells of the column. The rows stay quiet. The regions stay quiet.
Two 3s in one region. They share neither a row nor a column. A box-shaped Sudoku would not show you this miss in the same place. One 3 happens to be the digit that belongs there. Check flags the region.
What to play next
Easy finishes with singles. Medium adds pointing, and on an 8×8 or a 9×9 it adds claiming. Hard adds pairs and, on some grids, a triple.
- EasySinglesStart here if the walls are new. The first press is a cell with one digit left, then the last empty cell of a row, a column, or a region, then a digit with one home. The daily size is the 9×9 easy grid. On that size, the first press is often the only home in a line.Play Easy →
- MediumRegion and lineWhen the singles stop, see whether a digit inside one region is confined to one row or one column, and take it off the rest of that line. Claiming, the line read the other way, waits for an 8×8 or a 9×9. A 6×6 medium grid does not ask for it.Play Medium →
- HardPairs, then a tripleTwo cells that share two digits, or two digits that share two cells, and on some grids three cells that share three digits. An 8×8 hard grid is the same lesson. No guess.Play Hard →
4×4 comes in easy. 6×6 comes in easy and medium. 8×8 and 9×9 come in easy, medium, and hard. Try 6×6 easy, 8×8 medium, 8×8 hard, and 9×9 easy. The daily puzzle is a 9×9 easy grid: today’s Jigsaw Sudoku opens the same size and setting as 9×9 easy. Those grids finish with singles.
Print a Jigsaw Sudoku pack. A 4×4 or 6×6 sheet holds four puzzles. An 8×8 or 9×9 sheet holds two. Large print is one grid. 4×4 comes in easy. 6×6 comes in easy and medium. 8×8 and 9×9 come in easy, medium, and hard.
- GuideSudokuRows, columns and boxes, from singles to triples.
- GuideKiller SudokuCage sums and house totals do the work.
- GuideKakuroOne-way sums first, then short runs and longer lists.
- GuideFutoshikiSigns first, then chains, one home in the line.
- GuideCalcudokuOne-way cages first, then the rest of the line.
- GuideHashiCount bridges, never cross, connect every island.
- GuideBinairoSpot pairs, fill the gaps, balance every line.
- GuideStar BattleOne or two stars in every row, column and region.
- GuideSlitherlinkDraw one loop. Start from the 0s and the 3s.
- GuideNonogramsOverlap long clues, cross the gaps, and read the crossing line.
- GuideHitoriShade repeats, never side by side, keep white connected.
- GuideNurikabeGrow each island to its number and keep one sea.
- GuideLight UpLight every cell. Start beside the 4s and 0s.
- GuideShikakuEach number is an area. Start with the ones that fit one way.
- GuideMasyuTurn on black pearls, go straight through white ones.