When a grid stalls, the issue is usually messy candidates, not missing genius. The sections below follow a practical order from beginner habits to tougher patterns. If the rules still feel fuzzy, read Sudoku rules, then try lines on the Play sudoku board.
Scan for singles
Each pass, ask which row, column, or box is missing only one digit. If a cell's candidates collapse to a single value after crossing out peers, place it—that is a naked single.
On easier openings you may chain several singles in a row. Fill what is forced before you guess; the grid becomes easier to read.
Row-column-box crosses
For any empty cell, eliminate digits already used in its row, column, and box. What remains is your candidate list; one left means you can enter it.
When you select a cell, this site dims its row, column, and box and highlights matching digits elsewhere—use that view before scanning the whole board randomly.
Pencil marks
When two or three candidates remain, pencil them in instead of committing. Later placements may remove options—update notes as you go.
You do not need notes in every cell—focus on trouble spots and tight regions. If notes disagree with the board, Check or Undo beats forcing a digit.
Pairs and beyond
When singles dry up, look for pairs: two cells in a unit that share exactly two candidates can eliminate those digits from other cells in the row, column, or box.
Harder puzzles may need triples, X-Wing, and more. Hints on this site name the technique that fits the current board so you can map words to the grid.
Hints and check
Use Hint when you are stuck—read the explanation, then place the digit yourself. Use Check when something feels wrong, not after every entry.
Daily puzzle is good rhythm practice: one shared board per day lets you repeat the same scan order without random layouts pulling you off track.
Common questions
What should beginners practice first?
Scan for naked singles row by row, column by column, and box by box. Add systematic pencil marks once singles stop appearing.
Do I need nine pencil marks in every cell?
No. Note only cells where you are unsure. Pencil is a tool, not busywork.
Do hints name techniques?
Yes. Hints describe the logic in plain language (for example a hidden single) and highlight the cells involved.
Should I use Check or Hint first?
Check when you fear a mistake but do not know where. Hint when you cannot see the next move. Neither finishes the puzzle for you.
Is guessing okay on hard puzzles?
Classic grids here are meant to be logic-only. If you keep wanting to guess, rescan for singles and refresh pencil marks first.
What does the highlight around my selection mean?
The row, column, and box fade in, and cells with the same digit as your selection are emphasized for elimination.
Is Daily good for practice?
Yes. One puzzle per date is useful for comparing progress and repeating scan habits without random layouts every time.
Does Undo remove pencil marks?
Undo restores the entire previous board state, including digits and notes from your last action.
Do higher difficulties need advanced techniques?
Usually. Fewer givens mean singles run out sooner, so pairs and stronger patterns matter more. Medium is a solid training band.
How long until I get faster?
It varies, but a steady order—singles, pencil, then Hint—often cuts wasted clicks within a few grids. Daily helps build the habit.
