How SudokuLab works
A walk through one game and one lesson. You only need to know the basic rules of Sudoku to follow along.
Play a puzzle
- Start a puzzle. Open Play and choose Easy, Medium, Hard or Master. You can also import a puzzle by pasting 81 digits from a book or another app.
- Enter numbers and notes. Tap a cell, then a number on the pad or keyboard. Turn on Notes, or press M, to write candidates as pencil marks. Fill candidates writes them all in for you.
- Ask for a hint. Hint opens the coach on the easiest useful step on your board. Explain step by step plays that move on your own grid.
- Continue later. Your board is saved as you play. Next time, Play shows a Continue card with how many cells are still open.
Related answers: Numbers and notes · Saved progress
Follow a technique from example to challenge
Learn lists 25 techniques in three stages: Foundations, Advanced and Expert. Each one has its own page with three steps. Here is the second technique, the Hidden Single.
Hidden Single · Singles · Easy — A digit that has only one cell left in a row, column or box. That cell may still show other candidates, which is why the move is easy to miss.
Learn
The worked example highlights the cells where the digit cannot go, sentence by sentence, until only one cell is left in the unit.
Practise
On a taught position, or a fresh variation of it, find the cell and enter its digit.
Challenge
A complete Sudoku where the Naked Single runs out partway through and hidden singles get you going again.
Once you know a few techniques, Mixed practice gives you five unseen positions with the technique hidden: name it, then make its move.
Focused and Mixed challenges
A Challenge is a complete Sudoku for practising one technique. You choose the kind on the technique’s page.
- Focused — The board can be finished with this technique and the ones taught before it. One solving path using only those was checked to the end.
- Mixed — The board practises the technique the same way, then may need other techniques to finish. It lists them before you start.
Neither kind promises the technique is the only way through. Wrong final digits are refused and count as mistakes. Three mistakes end a Challenge. Pencil marks never count. Your Challenge and Play board are kept apart.
The board coach
Hint shows the easiest step that makes progress on your board, never the solution: a single before a pair, a pair before an X-Wing. It arrives in stages, and you can stop at any of them.
- Pattern. The cells that make up the pattern are highlighted.
- Reasoning. The coach explains in plain language why the pattern holds.
- Elimination. It shows which candidates the pattern removes. Remove them yourself, or let the coach do it.
- Explain step by step. Plays the move on your grid, with your cells and your digits.
To practise one family, choose it under Look for. To see everything at once, turn off Stepped hints in Settings → Coach.
