Practical tips for every skill level — from first-time solvers to players tackling expert puzzles.
Look for rows, columns, or boxes that already have 7 or 8 numbers filled in. The remaining cells are easiest to solve because fewer numbers are available.
Pick a single digit (start with 1) and find where it already appears on the board. Use those positions to eliminate it from rows, columns, and boxes — then find where it must go in the remaining areas.
SudokuSolve highlights conflicts in red immediately. If you see red, undo your last move and try a different number. Never leave conflicts on the board and continue.
Enable Pencil Marks mode to see every possible candidate for each cell. As you fill in numbers, candidates automatically narrow. A cell with one remaining candidate can be filled immediately.
If a number can only go in one row (or column) within a 3×3 box, it must stay inside that box. Cross it off from the rest of that row or column outside the box — this often unlocks a chain of deductions.
If two cells in the same row, column, or box both have exactly the same two candidates (e.g. {4, 9}), those numbers are reserved for those cells. Remove them from every other cell in that group.
Every cell belongs to a row, a column, and a box. When stuck, check all three. A number might be forced not by one constraint alone, but by the combination of all three eliminating every other option.
When SudokuSolve gives a hint, read the strategy name (Naked Single, Hidden Single, Pointing Pair) and understand why it works before applying it. Over time you'll start spotting those patterns yourself.
Each number you place changes the board. A cell that had multiple candidates might now have only one. After filling any cell, quickly re-scan its row, column, and box for new naked singles before moving on.