Sudoku Next-Move Hints | Technique Names and Reasons, Answer Check, Unique-Solution Test
A tool for when you are stuck on a Sudoku from a newspaper, magazine or app and want just the “next move” instead of the full answer. Enter the puzzle on the board and press “Next-move hint” to highlight the box, row or column to look at first. Press again to see which technique applies (Hidden Single, Pointing, Naked Pair, Naked Triple, X-Wing or Swordfish) and why it works. It supports candidate display, answer checking (wrong cells shown in red), the answer for a selected cell only, a list of solving steps from here to the end, a test of whether the puzzle has exactly one solution plus a difficulty rating, and automatic puzzle generation at the difficulty you choose.
Select a cell and press a digit. On a computer you can also use the number keys, arrow keys and Backspace.
Press this when you are stuck. It does not show the answer right away: first where to look, then which technique applies and why.
Load / create puzzles
See the solving steps from here to the end
Techniques used in hints (easiest first)
- Hidden Singleヒドゥンシングル・消去法
- In a box, row or column, only one cell is left where that digit can go.
- Naked Singleネイキッドシングル・候補が1つ
- Only one digit is left that can go in that cell.
- Pointingロックされた候補・ブロックから行列へ
- Within a box, the candidates for a digit all lie in one row (column). The digit can be removed from the rest of that row (column) outside the box.
- Claimingロックされた候補・行列からブロックへ
- Within a row (column), the candidates for a digit all fit in one box. The digit can be removed from the other cells of that box.
- Naked Pairネイキッドペア・二国同盟
- In a row, column or box, two cells have the same two candidate digits and nothing else. Those two digits can be removed from the other cells.
- Hidden Pairヒドゥンペア
- Two digits can go in only the same two cells within a row, column or box. Other candidates can be removed from those two cells.
- Naked Tripleネイキッドトリプル
- The candidates of three cells together consist of only three digits. Those three digits can be removed from the other cells of the same row, column or box.
- Hidden Tripleヒドゥントリプル
- Three digits can go in only the same three cells within a row, column or box. Other candidates can be removed from those three cells.
- X-WingX-Wing（エックスウィング）
- A digit’s candidates lie in the same two columns in each of two rows (a rectangle shape). The digit can be removed from the other rows in those two columns.
- Swordfish3行3列の井桁
- An X-Wing extended to 3 rows and 3 columns. If the candidates in three rows fit in the same three columns, the digit can be removed from the other rows in those columns.
- Guessing背理法・トライアンドエラー
- The techniques so far cannot decide it, so place a digit tentatively in a cell with few candidates and check whether a contradiction appears.
Difficulty guide: Easy = Solvable with Hidden Singles alone / Normal = Solvable by finding cells with only one candidate / Hard = Needs Pointing and Naked Pairs / Advanced = Needs Hidden Pairs, Naked Triples and X-Wing / Expert = Needs Swordfish / Guessing needed = There are points where logical techniques alone cannot make progress
ABOUT
About Sudoku Next-Move Hints | Technique Names and Reasons, Answer Check, Unique-Solution Test
Sudoku Next-Move Hints is a tool for when you are stuck on a Sudoku from a newspaper, magazine or app and want only the “next move” rather than the whole answer. Enter the puzzle on the board and press “Next-move hint” to highlight the box, row or column to look at first. Press again and it explains, in plain language, the technique to use (Hidden Single, Naked Single, Pointing, Claiming, Naked Pair, Hidden Pair, Naked Triple, X-Wing, Swordfish) and why a digit goes in that cell or why a candidate can be removed. Hints are found by trying the techniques people use on paper, from easiest to hardest, so you can reuse them when solving by hand. When no technique makes progress, it tells you that guessing (trial and error) is needed and shows only the answer of the cell with the fewest candidates. It also offers automatic candidate display, answer checking (cells that differ from the answer in red), the answer for a selected cell only, a list of solving steps from here to the end, a test of whether the puzzle has exactly one solution plus a difficulty rating, and automatic puzzle generation at the difficulty you choose.
How to use Sudoku Next-Move Hints | Technique Names and Reasons, Answer Check, Unique-Solution Test
- 1Choose “Enter a puzzle” and type the puzzle’s digits onto the board (you can also paste an 81-character puzzle to load it)
- 2Check that “Solutions” at the top right shows “1 (valid puzzle)”, then press “Solve this puzzle”
- 3As you solve, enter your own digits on the board (select a cell and use the digit buttons or the number keys on your keyboard)
- 4When you get stuck, press “Next-move hint” and think about the highlighted place (box, row or column)
- 5If you still cannot see it, press “More detail” to see the technique name and reason, and the digit that goes in or the candidates that can be removed
- 6Use “Place this move on the board” or “Remove these candidates” to apply it and keep solving. Use “Check answers” to find mistakes
Great for
- You are stuck on a newspaper or magazine Sudoku and want only the next move without looking at the answer page
- The hint feature in your Sudoku app just fills in an answer and you do not understand why
- You want to learn techniques such as Naked Pair, Naked Triple and X-Wing, including how to spot them, on a real board
- You want to check only which cells in your partly solved board are wrong
- You want to confirm that a puzzle you made has exactly one solution and is a valid puzzle
- You want to know how hard a puzzle is and which techniques it requires
- You want to solve a new puzzle at a difficulty you choose: Easy, Normal, Hard, Advanced or Guessing needed
- You want to practice Sudoku thinking with children or family, viewing the hints one level at a time
Good to know
- Hints are searched in the order “Hidden Single → Naked Single → Pointing / Claiming → Naked Pair → Hidden Pair → Naked Triple → Hidden Triple → X-Wing → Swordfish”, and the first move found is shown. If an easier technique can make progress, a harder one is never shown.
- When no technique makes progress, it says “guessing (trial and error) is needed” and shows just one answer: the cell with the fewest candidates. Advanced techniques such as XY-Wing and chains are not supported.
- If a digit you entered differs from the answer, it tells you before giving a hint, because logical solving from a wrong digit leads to contradictions.
- A puzzle with fewer than 17 given digits cannot have a unique solution. For a puzzle with two or more solutions, answer checking and answer display are unavailable.
- “Difficulty” is decided by the hardest technique needed to solve the puzzle from the start. It may differ from the “star rating” used by magazines and apps.
- Puzzles are generated so that they have exactly one solution and the empty cells are point-symmetric (the same shape when rotated 180 degrees). Advanced and Guessing-needed puzzles may take a few seconds to generate.
- The board, the digits you entered and the candidates you removed are saved only in this device’s browser and are never sent to a server.
Questions this tool answers
Use Sudoku Next-Move Hints | Technique Names and Reasons, Answer Check, Unique-Solution Test for searches like these:
- I am stuck on a Sudoku and want to know just the next move
- I want Sudoku hints without seeing the answer
- I want to know how to find Naked Pairs and Naked Triples in Sudoku
- I want to see an X-Wing on a real Sudoku board
- I want to check my Sudoku answers
- I want to check whether a Sudoku I made has only one solution
- I want to rate the difficulty of a Sudoku
- I want to generate Sudoku puzzles for free
FAQ
- Can you tell me only the next move without showing the answer?
- Yes. Press “Next-move hint” and it first highlights only “which box, row or column to look at”. Press again to see the technique name, the reason, and the digit that goes in (or the candidates that can be removed). You decide whether to apply it to the board.
- What is a Naked Pair in Sudoku?
- When two cells in the same row, column or box have exactly the same two candidate digits, those two digits are used up by those two cells. For example, if both cells have the candidates “3 and 7”, you can remove 3 and 7 from the other cells in the same column. A Naked Triple is the same idea with three cells and three digits.
- How do I find an X-Wing?
- Look for a row where a digit has candidates in only two places, then find another row where the same digit has candidates in only the same two columns. If the four cells form the corners of a rectangle, that is an X-Wing. You can remove that digit from the other rows in those two columns. It works the same way with rows and columns swapped. When this tool finds one, it highlights the four cells and explains.
- Can I check that a puzzle I made has only one solution?
- Yes. Enter digits in “Enter a puzzle” and the top-right “Solutions” shows “1 (valid puzzle)”, “2 or more” or “None”. The number of solutions is counted by having the computer check every possible way of filling the grid. It also shows the difficulty (Easy to Guessing needed), based on the hardest technique needed to solve it logically.
- What if I only want to know where the mistakes are?
- Press “Check answers” and the digits you entered that differ from the answer are shown in red, together with the number of correct cells and the number of remaining cells. The answers themselves are not shown.
- Can I load puzzles from other sites or apps?
- Yes. Paste a string of 81 characters, read row by row from the top left, with 0 or . for empty cells. Even if line breaks or separators are included, only digits and . are picked up. You can also copy the current puzzle or board in the same format.
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