Sudoku Made and maintained by Brian Hamilton and Karan Hamilton.
Brian builds the playable puzzle tools, while Karan helps test clarity, difficulty feel, and the player experience.
Playable puzzles and controls are tested in the browser for rule accuracy, usability, and a clear solving experience. See how we make and test puzzles, our editorial standards, or report a problem.
What is 8×8 Sudoku?
8×8 Sudoku is sudoku on a smaller grid: eight rows, eight columns and eight boxes, each box two rows tall and four columns wide. Fill the grid with the digits 1 to 8 so that:
- every row holds each of the eight digits once;
- every column does too;
- and so does every 2×4 box.
That is the whole rule. What changes from the classic grid is the shape of the boxes, and with it which squares see each other: every square shares a row, a column or a box with 17 others, against 20 on a 9×9 grid.
The boxes come in four bands of two rows, two boxes side by side in each, and in two stacks of four columns, four boxes on top of each other. So every row runs through two boxes and every column through four. The bands are where this grid differs most from the classic one, as the second figure below shows.
How do you find where a digit goes?
One digit at a time. Pick a digit, find every copy of it already on the board, and look at a box that still needs it: each copy rules out its own row and column. When only one empty square of the box is left, the digit goes there, whatever else that square could hold on its own. That is a hidden single:
The same sweep works along a row or a column: a digit with one place left in a line goes there. And a square whose row, column and box already hold seven different digits takes the eighth. Between them, those two moves finish every Easy and Medium board on this page.
What do the wide boxes give you?
A shortcut along each band. A box is only two rows tall, so the two boxes of a band share both their rows, and each row holds every digit once. A digit that is already in one box of the band therefore sits in one of the two rows, and the other box’s copy must take the other row. Half the box is ruled out at once:
It is a hidden single like the first, reached through the band: look along the band before you look down the columns. The same reasoning works down a stack, but with four boxes there it rules out less, so the bands are the place to start.
What do Hard and Expert boards add?
Fewer digits, first of all, and on Expert two more moves. When singles run out, put the digits each empty square can still hold in its pencil marks and look inside one box at a time. If a digit’s places in the box all lie in one row or column, the box’s copy of that digit is that line’s copy too, so it comes out of the rest of the line:
That is locked candidates. Hard boards are dug so that singles and locked candidates finish them, but with 24 digits given they rarely need more than singles: 196 of 200 Hard boards we dealt fell to singles alone. Expert boards are dug for one more move, the naked pair: two squares of one row, column or box that can each hold only the same two digits take those two between them, so no other square there can have either:
Expert boards are dug so that singles, locked candidates and naked pairs finish them, and they start with the fewest digits.
What went wrong with this page?
For most of 2026 it did not work. The first version, in April, took digits out of a full grid at random and never checked that what was left had only one answer: we dealt 160 boards from it and 115 had more than one — every Expert board among them. On such a board the game still marked a square wrong whenever it differed from the one answer it had stored, even where the other answer was just as right. A check was added after eleven days, and the change left two stray lines in the script. From then on the browser could not run it, and until October the page showed an empty board and buttons that did nothing.
The game was rebuilt in October 2026, on the generator rebuilt this year for the site’s letter, colour and word sudoku. It now takes a digit out only while the level’s own steps still solve the board, which also proves the board has exactly one answer, and in Chrome a new board appears in well under a tenth of a second at every level. A solver that knows singles, locked candidates, pairs, triples and the X-Wing finishes every board, and no level needs more than its own steps.
How do the four levels differ?
By how many digits are given, and by the steps a board is dug for. We dealt 40 fresh boards per level from the new generator, and 40 per level from the April one:
| Level | Given digits | Dug for | Singles alone finish it | April boards with more than one answer |
|---|---|---|---|---|
| Easy | 38 | singles | 40 of 40 | 9 of 40 |
| Medium | 30 | singles | 40 of 40 | 27 of 40 |
| Hard | 24 | + locked candidates | 40 of 40 | 39 of 40 |
| Expert | 18–20 | + naked pairs | 36 of 40 | 40 of 40 |
40 boards per level, fixed seed. Expert digs toward 18 digits as far as its steps allow and keeps the fewest of up to six tries: 18 to 20, median 18. On 200 more boards per level, singles alone finished 196 Hard and 174 Expert boards; one Hard board could not be finished without locked candidates, and among the Expert boards six needed locked candidates and three needed pairs.
On this grid the levels differ mostly in how many digits you are given. Easy, Medium and Hard almost always fall to singles alone, and each is harder than the last because it starts with fewer digits — 38, 30, 24. Expert, at about 18, is where locked candidates and pairs turn up, on about one board in eight; on Hard they were needed once in 200 boards.
A digit comes out only while the level’s steps — singles on Easy and Medium, plus locked candidates on Hard, plus naked pairs on Expert — still fill the grid, and each step only strikes digits that cannot go where they are struck. We re-counted all 160 new boards with a separate counter written for the purpose: every one had exactly one answer, the stored one.
Which level should you play?
Start on Easy, where the page opens, if 8×8 is new to you. Easy gives 38 digits and Medium 30, and both fall to singles alone; Medium is the step to take once Easy goes quickly.
Read along the bands before you read down the columns: for each digit in one box of a band, find the row its copy must take in the other box. Then sweep one digit at a time: select a square that holds it and every copy lights up. Hard asks for the same moves with fewer digits to start from, and Expert adds the two above.
What do the buttons do?
Select a square, then a digit; the page opens on Easy. Selecting a square highlights its row, its column and its box, and a wrong digit is marked the moment it goes in. Under the grid:
- Notes turns pencil marks on and off. A correct digit clears itself from the notes of its row, its column and its box; a wrong one leaves the other squares’ notes alone.
- Erase clears the selected square, and pressing the same digit twice does the same.
- Undo takes back the last change to a square, though not the notes a correct digit cleared elsewhere, and not the Mistakes count.
- Hint fills one square with its answer, picked at random rather than the square you could work out next.
- Solve asks first, then fills the grid and stops the timer.
- New Game deals another board at the level you are on; the level buttons deal one at theirs.
From a keyboard: 1–8, the arrow keys, Backspace or Delete and Ctrl+Z; 9 does nothing, and shortcuts such as Ctrl+1 are left to the browser. The board is saved in this browser after every move, so it is waiting when you come back.
Where to go next
The other sizes here work the same way: 4×4 Sudoku and 6×6 Sudoku below this one, and 12×12 Sudoku and 16×16 Sudoku above the classic grid.