Insert your number or tap the number on the pad below to place it.
Use the tools below:
↩ Undo Take back your last move.
✏️ Notes Toggle pencil mark mode to write small candidate numbers.
✓ Check Highlight any incorrect numbers in red.
💡 Hint Fill in a random empty cell with the correct number (3 per game).
↻ New Start a fresh puzzle at the current difficulty.
🎉
Puzzle Complete!
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Strategy 1 · Basic
Last Free Cell
If a row, column, or 3×3 box has eight of its nine cells filled, the remaining empty cell must contain the only missing digit. Always scan for nearly-complete units first — they are the quickest wins on the board.
Strategy 2 · Basic
Scanning & Cross-Hatching
Pick a digit — say 2. Find every row and column that already contains a 2 and mark them as blocked. Any cell at the intersection of two blocked lines is eliminated. If only one cell in a 3×3 box is left unblocked, that cell must hold your 2. Repeat for every digit 1–9.
Strategy 3 · Basic
Last Possible Number
For any empty cell, check which digits already appear in its row, column, and 3×3 box. If together they cover eight of the nine digits, the one remaining digit must go in that cell.
Strategy 4 · Basic
Hidden Single
A digit that can only be placed in one cell within a row, column, or box — even though that cell appears to have multiple options. For each unit, ask yourself: "Is there any digit that fits in only one cell here?" If yes, that digit belongs there immediately.
Strategy 5 · Basic
Near-Complete Lines
When a row or column has only 2–3 empty cells remaining, list the missing digits. Then use constraints from the intersecting rows, columns, and boxes to determine which digit goes in which remaining cell.
Strategy 6 · Intermediate
Pencil Marks (Candidate Numbers)
In each empty cell, write in small digits every number from 1–9 that is not already present in that cell's row, column, or box. Keep candidates updated as you place digits — erase any candidate in the same row, column, or box whenever a new digit is confirmed.
Strategy 7 · Intermediate
Naked Single
Any cell with only one candidate remaining must contain that digit. After setting up pencil marks, scan for naked singles continuously — they are the most immediate placements available and often trigger chain reactions.
Strategy 8 · Intermediate
Naked Pair
If two cells in the same row, column, or box contain exactly the same two candidates — and only those two — then those digits must occupy those two cells in some order. Eliminate both digits as candidates from every other cell in that unit.
Strategy 9 · Intermediate
Hidden Pair
Two specific digits appear as candidates in exactly two cells within a unit, but those cells also contain other candidates. Because the two digits must occupy those two cells, remove all other candidates from those two cells — leaving only the pair.
Strategy 10 · Intermediate
Locked Candidates
Type 1 (Pointing): if a digit's candidates within a 3×3 box all fall in the same row or column, eliminate that digit from all other cells in that row or column outside the box. Type 2 (Claiming): if a digit's candidates in a row or column all fall within one box, eliminate that digit from the rest of the box.
Strategy 11 · Intermediate
Naked Triple
Three cells in the same unit whose candidates together consist of only three digits — each cell may hold two or three of them. Those three digits must go into those three cells, so eliminate them from all other cells in the unit.
Strategy 12 · Advanced
X-Wing
Find a digit that appears as a candidate in exactly two cells in each of two different rows, where those cells fall in the same two columns. The four cells form a rectangle. The digit must occupy one diagonal pair or the other — eliminate that digit from all other cells in those two columns.
Strategy 13 · Advanced
Swordfish
An extension of X-Wing using three rows and three columns. A digit appears in two or three cells per row, and all those cells are confined to the same three columns. The digit can be eliminated from all other cells in those three columns.
Strategy 14 · Advanced
Skyscraper
A digit appears in exactly two cells in each of two rows. The two pairs share one column — the "base." The other two cells (the "roof") are in different columns. Any cell that shares a row, column, or box with both roof cells cannot contain that digit.
Strategy 15 · Advanced
XY-Wing (Y-Wing)
Three cells, each with exactly two candidates, form a pattern: a pivot cell with candidates {X,Y}, and two pincer cells with candidates {X,Z} and {Y,Z}. The pivot shares a unit with each pincer. Any cell that shares a unit with both pincers cannot contain Z — because regardless of how the pivot resolves, one pincer will always produce Z.
Strategy 16 · Advanced
Unique Rectangle
A valid Sudoku has exactly one solution. If four cells form a rectangle spanning two rows, two columns, and two 3×3 boxes — all sharing the same two candidates — a "deadly pattern" would create two solutions. Use this to eliminate candidates or confirm placements that break the pattern.
Strategy 17 · Advanced
Forcing Chains
Select a cell with exactly two candidates and follow two chains of logical consequences — one for each candidate. If both chains lead to the same conclusion for some other cell, that conclusion is confirmed true. The most powerful general technique but also the most demanding to execute.