Sudoku Written and built by Brian Hamilton. Reviewed by Karan Hamilton.
Brian handles the technical puzzle logic, while Karan checks the page for clarity, usability, and player experience.
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Wordoku Solver: solve letter Sudoku puzzles online
This free Wordoku Solver is built for 9x9 letter Sudoku puzzles, including newspaper Wordoku, printable worksheets, classroom puzzles and hidden-word grids. Enter the nine letters your puzzle uses, add the given clues, and the solver completes the grid with ordinary Sudoku logic. You can solve the whole puzzle, fill one cell at a time, import an 81-character string, export a clean copy, and check whether the puzzle has a single answer.
Wordoku looks different from classic Sudoku because it uses letters instead of digits, but the rules are the same. Each row, each column and each 3x3 box must contain all nine symbols exactly once. A puzzle might use a word such as WORDUKABC, a themed set of letters, or a completely arbitrary nine. The solver maps those letters to internal values, solves the logic, then converts the answer back into your letters.
That makes it useful for Wordoku, letter Sudoku, alphabet Sudoku and word Sudoku without translating the grid into numbers by hand. The aim is not only the final answer, but to help you find mistakes and see the next move when a letter grid gets stuck.
What a Wordoku actually is
Most Wordoku puzzles are a 9x9 grid divided into nine 3x3 boxes. Instead of the digits 1 to 9 you place nine different letters. Here is a real one, generated and then checked for how many answers it has.
That last sentence is the whole point. The logical structure is Sudoku; the letters are a costume. Because the rules are identical, Wordoku rewards the same habits: scanning, candidate notes, singles, pairs and box-line reductions.
What does change is recognition. Digits have an order everyone already knows, so a missing 7 announces itself. An arbitrary set of nine letters has no such order, and some letters look alike at a glance. That is a real difficulty, but it is a difficulty of reading, not of logic — which is why writing the nine letters in a fixed order beside the puzzle, and checking candidates in that order every time, helps so much.
The hidden word, and what it is not
Many published Wordoku puzzles arrange their nine letters so the finished grid spells a word somewhere — often down the main diagonal. Here is the puzzle above, completed.
This is worth being blunt about, because the presentation invites the opposite conclusion: the hidden word is not a solving aid, and this solver does not use it. Its rule check looks at rows, columns and 3x3 boxes, and nothing else. There is no diagonal constraint anywhere in it.
A setter produces a grid like this by pinning the diagonal before generating — fix those nine cells to the nine letters in the order you want, then fill the rest as usual. It costs nothing logically, which is exactly why it works as decoration. If a puzzle genuinely required its diagonals to hold all nine symbols, that would be a different variant with its own X-Sudoku solver, and this page is not it.
Setting the nine letters
The letters box takes the symbols printed with your puzzle. It is more forgiving than it looks: input is upper-cased, and anything that is not a letter — spaces, commas, punctuation — is stripped out. Repeats are dropped rather than rejected, so pasting a word with a doubled letter will not produce an error by itself.
What it does require is that nine distinct letters survive that cleanup. This is where hidden-word puzzles trip people up: a nine-letter word with a repeated letter only supplies eight distinct symbols, so puzzle makers add a substitute. If your word is short of nine unique letters, look for the full symbol set printed alongside the grid rather than trying to make the word itself work.
How to use the Wordoku solver
- Type the nine letters into the Letters box. Order is up to you — it only decides the order of the letter buttons, not the answer.
- Select a cell and enter the given clues with the letter buttons or the keyboard.
- Use Solve for the completed grid, and for the answer to whether the puzzle has just one.
- Use Step to fill in one cell at a time — though not the cell you might expect. See the section below.
- Use Erase to clear a selected cell, and Clear grid to start again with the same letters.
- Use Import to paste an 81-character puzzle, and Export to copy the current grid back out.
Put only the fixed clues from the original puzzle into the grid before solving. Avoid entering guesses as though they were clues: a wrong guess can make a perfectly good puzzle look impossible. If you do want to test one, enter it, solve, and be ready to erase it when the solver reports a contradiction.
Importing and exporting Wordoku puzzles
The import box takes 81 characters read left to right, top to bottom — row one, then row two, and so on. Use your puzzle letters for clues and 0 or a dot for empty cells. Whitespace is stripped before counting, so a puzzle pasted as nine tidy rows still reads as one 81-character string.
There is a convenience here the page has never mentioned: if the string itself contains exactly nine different letters, the solver adopts them automatically and fills in the Letters box for you. You only need to set the letters by hand when the clues do not use all nine — which is common in sparse puzzles, and is why an import can be rejected as invalid even though the string is exactly 81 characters long.
Export gives you the same 81-character form from the current grid, using 0 for each blank. You can export the starting clues, a half-finished grid, or the completed answer, which makes it easy to compare two versions or send someone the exact state instead of a screenshot.
You can also link straight to a puzzle, which the page has never mentioned either: add ?puzzle= and the 81-character string to this page’s address and the grid loads and is validated as the page opens. Export gives you the string to paste in.
Why not just map the letters to digits
You can solve a Wordoku with an ordinary 9x9 Sudoku solver by mapping each letter to a number, and the answer will be correct, because the two really are the same puzzle. The cost is the translation. It is easy to swap two symbols, lose track of the mapping halfway through, or copy the finished digits back onto the wrong letters — and every one of those errors looks like a puzzle fault rather than a bookkeeping one.
Keeping the puzzle in its printed symbols removes that whole class of mistake. The board you check against your paper is the board you typed, in the letters that are on the page.
What the solver checks before it searches
Before solving, the tool checks the letter set is nine distinct symbols, that every clue on the board belongs to that set, and that no letter is repeated in a row, a column or a 3x3 box. If a clue clashes, the message names the letter and where. Those checks run first because they catch the copying mistakes that would otherwise look like an unsolvable puzzle.
They look for repeats and membership, and nothing else, so a grid can pass them cleanly and still have no answer. The search finds that out afterwards. That is why "no solution" and "duplicate R in row 4" are different messages: the second points at a cell, while the first only means the whole search came back empty-handed.
When to use Step instead of Solve
Step is the button for when you want help without giving the answer away, and it is worth knowing what it actually does, because it is not what the name suggests. Step solves the entire grid in the background first, then fills the next empty cell in reading order — left to right, top to bottom — copying from the answer it already holds. It names the row, the column and the letter, and says nothing about why.
So it is not picking a placement you were meant to find, and there is no elimination behind its choice to go hunting for. The cell it fills is simply the first empty one. What Step is good for is getting unstuck: reveal one letter, then work out for yourself which row, column or box forced it, and carry on by hand from there.
Solve is the better choice when you want an answer key or a quick check. It is also the only route to the uniqueness result: once it finds a completed grid it goes back to your original clues and searches for a second answer, then reports one solution or several. Stepping to the end never produces that message.
Wordoku strategies that work by hand
Start with the densest parts of the grid. A row, column or box holding five or six letters has few gaps left, so a forced placement is easier to find. Make a short candidate list for the empty cells and cross off letters already used in the same row, column and box.
Then look for the singles. A naked single is a cell with only one possible letter. A hidden single is a letter with only one possible cell in a unit, and it can be placed even when that cell still appears to have several candidates.
Box-line reduction is the most useful mid-level technique here: if a missing letter in a 3x3 box can only sit along one row, that letter comes off the rest of the row outside the box, and the same works for columns. Naked pairs and hidden pairs work exactly as they do with digits — two cells restricted to the same two letters, or two letters restricted to the same two cells.
None of this is Wordoku-specific, and that is the point. If a letter puzzle feels harder than a number puzzle of the same grade, the difficulty is almost always in reading the symbols rather than in the deductions.
Common Wordoku errors and how to fix them
The most common error is a letter set that does not yield nine distinct symbols — usually a hidden word with a repeated letter. Use the full symbol set printed with the puzzle rather than the word. Case and spacing are not a problem: the box upper-cases what you type and throws away anything that is not a letter, so "w o r d u k a b c" and "WORDUKABC" are the same input.
If the solver reports no solution, check the clues before assuming the puzzle is broken. Look for a repeated letter in a row, column or box, and make sure every clue belongs to the letter set. If you imported a string, count the characters and confirm blanks are 0 or dots: one missing blank marker shifts every later clue into the wrong cell, which turns a valid puzzle into an impossible one.
If it reports multiple solutions, the clues are too sparse to force one answer. That is useful to know either way — if you are making the puzzle, restore a clue; if you are solving a published one, a clue was probably missed while copying.
Wordoku for teachers, printables and puzzle makers
Wordoku suits classrooms because it carries vocabulary alongside the logic. Teachers can pick topic words, names or lesson themes and keep the Sudoku structure underneath. The solver checks the finished grid before the worksheet goes out and produces the answer key at the same time. For younger classes, the smaller grids in Sudoku for kids are an easier starting point.
For puzzle makers it is a quality-control step. Verify the clue set, confirm the solution, export a compact string, and keep the answer in your notes. If you build several difficulty levels, use the solver to check whether removing a clue has created a second solution — fewer clues is not automatically better, and the best Wordoku is sparse enough to be interesting while still forcing one fair answer. If you want puzzles on paper rather than screen, there are printable Wordoku sets ready to go.
The solver is free, runs entirely in your browser and needs no account. Nothing is kept between visits, so export a grid before you leave if you want to keep it.