Sudoku strategy: the 5 techniques that solve 90% of puzzles
• ~7 min read
You don't need a 30-page solver's manual. Five techniques — applied in the right order — will finish almost every Easy and Medium Sudoku puzzle, and most Hards. Here they are, in the order I use them.
1. Scanning (the warm-up)
Pick a digit — say 1. Find every box that already has a 1. For each box that doesn't, look at which rows and columns are blocked by an existing 1. If only one cell in the empty box is free, place a 1 there. Repeat for 2, 3, …, 9.
Scanning alone finishes most Easy puzzles. It costs nothing — you don't even need to write candidates yet.
2. Naked singles
For each empty cell, list which digits 1–9 could possibly go there (no conflict in row, column, or box). If a cell has only one possibility, place it. Then repeat — because placing one digit often makes another cell a naked single too.
On SudokuGlyph, turning on Auto-notes fills these in for you, but it counts as a tool used. Doing it mentally is faster once you've practiced.
3. Hidden singles
Look at a row, column, or box. If only one cell in that group can contain a particular digit (even if that cell has lots of other candidates too), place it.
Example: in box 1, the digit 7 is only possible in one specific cell — even though that cell could also hold 2 or 5 or 9 by row/column logic. Place the 7 anyway. This is the most commonly missed beginner technique.
4. Naked and hidden pairs
Look for two cells in the same row, column, or box that share exactly the same two candidates — say both can only be {4, 7}. You don't know which is which, but you do know that no other cell in that group can contain 4 or 7. Eliminate them.
Hidden pairs work the same way in reverse: if two digits can only appear in the same two cells of a group, those cells must hold exactly those two digits — eliminate every other candidate from them.
5. Box/line reduction (pointing)
Inside a single 3×3 box, if all candidates for a particular digit lie in the same row (or column), then that digit must end up somewhere in that row inside the box — which means you can eliminate it from the rest of that row outside the box.
This is the technique that breaks open Hard puzzles. It's harder to spot, but worth practicing because it's pure deduction — no guessing.
When to switch tools on
Notes mode is your friend from move ~20 onwards. Conflict highlighting is for spotting your own typos, not solving — keep it off until you're stuck. Auto-notes and Candidates are powerful but they count against your "tools used" stat. Use them when you genuinely want the answer; do the puzzle clean when you want to improve.
Practice playlist
Three weeks of daily Easy → Medium → Hard, in that order, will internalise these techniques. Play the same difficulty for a full week before moving up. Resist the urge to switch when it gets boring — boredom is the sign you've learned the pattern.