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 Expert Sudoku here?
Expert is the hardest level our generator deals: classic sudoku starting from 22 to 25 of the 81 squares (23 on most boards), with exactly one answer. On top of naked and hidden singles it asks for two steps: locked candidates and naked pairs. It never asks for more. The fish, wings and chains that many sites file under “expert” belong to our Evil and Extreme puzzles, which come from a different source; more on those below.
What does an Expert board ask of you?
We dealt 200 Expert boards from this page’s own generator and tried each with one step at a time. Singles alone finished 135 of them. Locked candidates finished 47 more, and the last 18 needed a naked pair. Thirty-one boards could not be finished without locked candidates even with pairs allowed, so neither step is optional. Nothing past naked pairs was needed on any board.
| Level | Given digits | Singles alone finish | What the rest need |
|---|---|---|---|
| Easy | 40 | 200 of 200 | Nothing more |
| Medium | 32 | 200 of 200 | Nothing more |
| Hard | 26 | 171 of 200 | Locked candidates finish all 29 |
| Expert | 22–25 (median 23) | 135 of 200 | Locked candidates finish 47 more; naked pairs the last 18 |
200 boards a level, dealt by this page’s own generator and measured on 10 October 2026; every one had exactly one answer, counted by a separate solver. “Singles” means naked and hidden singles together. Nothing past naked pairs was needed on any board.
So an Expert board is a Hard board with fewer digits and one more tool. If locked candidates are new to you, the pointing pairs and box/line reduction guides cover both directions.
What is a naked pair?
A naked pair is two squares in one row, column or box that can each hold only the same two digits. Between them they take both digits, so neither can go anywhere else in that house. In the board above R3C2 and R3C5 hold only 4 and 7, which clears both from the rest of row 3. Notice how little the singles did on this board before the pair: Expert boards often need their extra steps early. The naked pairs guide has more.
Look in the houses with the fewest gaps and the squares with two candidates. Two of those in one house with the same two digits are a pair. Keep your notes clean: a candidate you forgot to strike turns a pair into three digits, and the pattern vanishes.
Why do Expert boards start with 22 to 25 digits?
The generator aims at 22. It takes digits away one at a time, keeping each removal only while the board still has one answer and singles, locked candidates and naked pairs can still finish it, and it tries up to six times, stopping as soon as a board reaches 22 and otherwise keeping the one with the fewest digits. Of our 200 boards, 39 reached 22, 107 stopped at 23, 53 at 24 and one at 25.
Fewer digits is not the same as harder, though. A 23-digit board that falls to singles is easier than a 26-digit board that needs a chain: our Evil puzzles carry a median of 26 digits, the same as Hard, and they are far harder than anything on this page.
Where do X-Wing, Swordfish and XY-Wing come in?
Not here. They come in on Evil Sudoku, whose puzzles come from a bank of 5,000 chosen for how hard they are to solve. We ran every one of them through the eighteen techniques our helper knows, always taking the simplest move left: an X-Wing was that move at some point in 644 of them, a Swordfish in 122, an XY-Wing in 1,743 and simple colouring in 710, and hidden pairs in 1,863. Even with all eighteen, 1,345 of the 5,000 still stall: Evil is where the chains begin.
Extreme Sudoku goes further again. On 4,980 of the 5,000 puzzles in its bank, the same eighteen techniques cannot make a single move. Every one of them still has exactly one answer; they just need longer reasoning than any named pattern.
Has this page always dealt boards like these?
Always one answer: the page went up on 7 May 2026, after the generator began checking for that. But until 10 October 2026 nothing checked how a board could be solved. Measured then, 11 of 40 Expert boards needed more than singles, locked candidates, pairs and the fish patterns our solver tries, and Expert landed anywhere from 22 to 27 digits, most often 25. This page told you that “guessing should not be required” and that you might need X-Wing, Swordfish, XY-Wing, XYZ-Wing, colouring or chains. Since 10 October every Expert board is finished by singles, locked candidates and naked pairs, and the generator checks that before you see it.
What do the buttons do?
- Notes switches the keypad to pencil marks, and Start Notes fills every empty square with the digits it can still hold, in one go.
- Hint picks a square at random from the ones that are empty or wrong and puts its answer in. It does not explain the step and it is an ordinary move: Undo takes it back.
- Undo and Redo step back and forward through your moves (Ctrl+Z and Ctrl+Y, or Cmd on a Mac); Erase clears the selected square.
- A wrong digit turns red and adds one to the mistake count. There is no limit: the count never ends the game.
- Solve asks before it fills the grid. New Game deals another Expert board, and the level buttons above the grid switch level without leaving the page.
- The timer starts when the board is dealt and runs until it is finished. Expert boards take the generator a few tens of milliseconds to dig; the others take a few.
Where next?
For the steps beyond naked pairs, play Evil. On the main daily sudoku both Saturday and Sunday are Expert, the same board for everyone. Hard is there when you want locked candidates without pairs. And the sudoku trainer drills any of the eighteen techniques on real boards, one pattern at a time.