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 Wordoku?
Wordoku is sudoku played with nine letters instead of nine digits, and the nine letters are those of a word. Fill the 9×9 grid so that:
- every row holds each of the nine letters once;
- every column does too;
- and so does every 3×3 box.
The letters change with every board. The buttons under the grid and the Letters bar above it show them in alphabetical order, and the word they make is hidden on the diagonal from the top-left corner to the bottom-right; finish the board, or press Solve, and the bar spells it out. Otherwise it is the same puzzle as Letter Sudoku, which always uses A to I, and Alphabet Sudoku, which draws nine letters at random: every sudoku technique works here letter for letter.
Every word on the list has nine different letters, so this diagonal always holds each letter exactly once — half the extra rule of X-Sudoku, which asks it of both diagonals, and true on every board here though nothing announces it. You may use it, and it is sound. You never need it: every board is dug so that rows, columns and boxes alone finish it.
Where is the word, and does it help?
The word is written down the diagonal, in order, before the rest of the grid is filled in around it, so on every board the diagonal of the answer spells it:
That makes the word the strongest tool on the page, if you can find it. Only a few of its letters are given — a median of 4 of the 9 on Easy and Medium boards, 3 on Hard and 2 on Expert, over 40 boards per level — and the rest of the diagonal comes free once you know it. With the diagonal filled in, singles alone finished every one of the 160 boards we dealt, Hard and Expert included.
The catch is that nine letters can make more than one word. ALGORITHM and LOGARITHM use the same nine; on the board above, the given A in the top-left corner settles it, because LOGARITHM would put an L there. Where nothing on the board settles it, the word you see is a guess, and a wrong letter costs a mark on the Mistakes counter the moment it goes in.
How do you find where a letter goes?
One letter at a time. Pick a letter, 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 letter 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 letter with one place left in a line goes there. And a square whose row, column and box already hold eight different letters takes the ninth. Between them, those two moves finish every Easy and Medium board on this page.
What do Hard boards add?
Locked candidates. When singles run out, put the letters each empty square can still hold in its pencil marks and look inside one box at a time. If a letter’s places in the box all lie in one row or column, the box’s copy of that letter is that line’s copy too, so it comes out of the rest of the line:
It works the other way round as well: a letter confined to one box within a row or column comes out of the rest of that box. Hard boards are dug so that singles and locked candidates finish them.
And Expert boards?
Naked pairs. Two squares of one row, column or box that can each hold only the same two letters will take those two letters between them, whichever way round, so no other square of that row, column or box can have either:
Expert boards are dug so that singles, locked candidates and naked pairs finish them, and they start with the fewest letters.
Were the boards on this page fair?
Not for their first twelve days. From 1 April 2026 the generator took letters out without checking anything, and 146 of 160 boards we dealt from that first version have more than one answer. From 13 April it checked every letter it took out with a full search, and we re-counted 160 of its boards with a separate counter to confirm it: each had exactly one answer. What it never checked was how a board would be solved. Each level only had a number of letters to leave, so the names meant less than they said. Expert was meant to leave 22 and managed it on 2 boards in 40, leaving a median of 24, close to Hard’s 26. And a solver that knows singles, locked candidates, pairs, triples and the X-Wing could not finish 31 of the 160 boards — 5 Medium, 18 Hard and 8 Expert — though the page promised that no guessing was ever needed.
The generator was rewritten in October 2026, the same fix as Letter Sudoku’s, which dealt from almost the same code. It now takes a letter 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 under a tenth of a second at every level, faster than before on Hard and Expert. Two keys were wrong as well: Ctrl+Z typed a Z instead of undoing whenever Z was one of the nine letters, and Ctrl+C typed a C.
How do the four levels differ?
By how many letters 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 old one:
| Level | Given letters | Dug for | Singles alone finish it | Old boards beyond our solver |
|---|---|---|---|---|
| Easy | 40 | singles | 40 of 40 | 0 of 40 |
| Medium | 32 | singles | 40 of 40 | 5 of 40 |
| Hard | 26 | + locked candidates | 36 of 40 | 18 of 40 |
| Expert | 22–24 | + naked pairs | 34 of 40 | 8 of 40 |
40 boards per level, fixed seed, words from the English list. Expert digs toward 22 letters as far as its steps allow and keeps the fewest of up to six tries: 22 to 24, median 23. On the new boards nothing past naked pairs was ever needed: two Hard boards could not be finished without locked candidates, and one Expert board not without pairs.
At the top the new levels are easier than the old ones, and fair all the way down. Most Hard and Expert boards now fall to singles alone, and what makes them harder is having fewer letters to start from — 26, and about 23 — against Medium’s 32. The old Hard and Expert were harder mainly because nearly a third of their boards needed more than any level here teaches.
A letter 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 letters 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, and on every one the diagonal spelled the word.
Which level should you play?
Start on Easy if sudoku is new to you, or on Medium if you know it with numbers. Easy gives 40 letters and Medium 32, and both fall to singles alone. The page opens on Medium.
Read the Letters bar first and try for the word; one you are sure of fills the diagonal. Then sweep one letter at a time: select a square that holds it and every copy lights up. With a new set of letters on every board, going through them in the order of the buttons makes sure none is skipped. Hard and Expert then add the two moves above, on boards with fewer letters to start from.
What do the buttons do?
Select a square, then a letter; the page opens on Medium. Selecting a square highlights its row, its column and its box, and a wrong letter is marked the moment it goes in. Under the grid:
- Notes turns pencil marks on and off. A correct letter 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 letter twice does the same.
- Undo takes back the last change to a square, though not the notes a correct letter 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, stops the timer and spells the word in the Letters bar.
- New Game deals another board, its word picked afresh, at the level you are on; the level buttons deal one at theirs.
From a keyboard: the nine letters themselves, or 1–9 for the buttons in order, the arrow keys, Backspace or Delete and Ctrl+Z; other shortcuts such as Ctrl+C are left to the browser. Finish a board and the word lights up along the diagonal and is named in the message. The board is saved in this browser after every move, so it is waiting when you come back.
Where to go next
The Daily Wordoku deals one board a day, the same for everyone, from the same generator: Easy on Monday and Tuesday, Medium on Wednesday and Thursday, Hard on Friday and Expert at the weekend. For a Wordoku from a newspaper or a book, the Wordoku Solver solves one you type in, and there are printable Wordoku sheets for paper.