How to use the Sudoku solver
Use this tool when you have a standard 9×9 Sudoku from a book, newspaper, or another puzzle source and want to check its answer. Enter only the printed clues, or enter your current progress if you deliberately want to test those extra numbers. The solver treats every number you enter as a fixed constraint. It cannot tell a printed clue from a guess, so an incorrect guess can make an otherwise valid puzzle impossible. Keep your original puzzle nearby for comparison.
Enter, solve, and compare
Gray digits form a solvable example. Solve it immediately, or select any cell to clear the whole example and enter your puzzle. Use 1–9; unknown cells stay blank. The example returns only when every cell is empty and you leave a cell. Clear removes your entries and answer, then shows the example again. Arrow keys move between cells, Tab moves through the form, and Backspace or Delete removes a value. Zero is not a blank-cell marker. Solving checks the current grid; changing the input invalidates the previous answer and Copy stays unavailable until another successful solve.
What the result means
A standard Sudoku uses the digits 1–9 once each in every row, every column, and each outlined 3×3 box. The solver preserves all your entered digits and searches for completions that satisfy these three rules. Exactly one solution means the search finished without finding another completion. More than one solution means at least two different completions were found; the displayed grid is only one of them. It is not a uniquely determined answer. No solution means the search finished without any completion that fits all your clues.
Reading and copying the answer
The completed grid appears before the explanation of its status. Original clues are bold and underlined, so they are distinguishable without relying only on color. The input grid remains editable and unchanged by solving. Copy solution copies the status and nine rows of digits separated by spaces, ready to paste into a plain-text note. Editing any input immediately clears the previous result and disables copying until you solve again. A failed clipboard request leaves the answer visible for manual selection.
Example 1: a nearly completed puzzle
Consider the completed row 5 3 4 6 7 8 9 1 2. If its third cell is blank while the other 80 cells form a valid completed puzzle, the missing digit must be 4. The result fills that cell and preserves every given number. The built-in example is also uniquely solvable: after solving it, the first answer row is 5 3 4 6 7 8 9 1 2. Use it to check the input and output flow before entering your own puzzle.
Example 2: ambiguity and mistakes
If you remove every 1 and 2 from any completed standard grid, swapping those two digits produces another valid completion. Such an input therefore has multiple solutions, even though none of its remaining clues conflict. By contrast, entering 5 in both the first and second cells of one row creates a direct duplicate, which is marked before a search starts. A puzzle can also be impossible without any immediate duplicate, because its remaining constraints cannot all be satisfied.
Limits and troubleshooting
This page supports standard 9×9 Sudoku only. It does not apply diagonal, killer-cage, irregular-region, or other variant rules. Each cell accepts one digit; letters, spaces, multiple digits, and zero are flagged rather than silently changed. Search stops after 150,000 search calls or about 1.5 seconds of worker time, with an additional browser timeout. Reaching a limit is an unresolved result, never proof of no solution or uniqueness. Check for omitted clues and transcription mistakes before trying again. The puzzle is processed locally; there is no account, photograph upload, puzzle generator, or step-by-step teaching mode.
Why does my puzzle have several answers?
Clues may be missing, or the puzzle may genuinely be ambiguous. Compare the entire input with the original. Adding an arbitrary number can force an answer, but does not establish that it is the intended answer.
Can I check my unfinished attempt?
Yes. Entering your added numbers checks whether they can coexist with all the other entries. To test the original puzzle alone, remove your guesses first. The tool does not identify which nonduplicated guess caused a contradiction.
Will solving overwrite my original numbers?
No. The answer is displayed in a separate grid, and all entered numbers are preserved in every reported solution. Editing or clearing the input discards the old result so you cannot accidentally copy an outdated answer.
Is my puzzle saved when I close the page?
No. This solver keeps its current grid in the open page only. Copy a result you want to retain before closing or reloading. Changing language navigates to another page and also clears this unsaved grid.
Does this explain human solving techniques?
No. It checks the rules and searches for valid completions. The order in which the search finds numbers is not a human-style explanation or a measure of puzzle difficulty.