Use this free sudoku investigator and solver to learn how some of the more advanced techniques of solving sudokus. You can load and save puzzles, use simple solving techniques automatically, and practise with harder puzzles. You could even write your own sudoku puzzles. NB. This is a Beta version. I hope to add to and strengthen it in the future, as well as publishing a few of my own puzzles.

Instructions below   Print this grid

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Compose a sudoku puzzle by clicking and dragging numbers from the left-hand column and dropping them into the grid.

Clicking on a number already on the grid will delete it.

Investigate more fully by checking or unchecking the "candidates" box at the top to see or hide all the possible candidates for each cell.

The "solve" button makes an attempt to enter values using basic solving techniques. It will solve most simple sudoku puzzles and even some harder ones. It will get as far as it can and stop, letting you find a way forward using intermediate and advanced techniques. Try it.

Pressing the "clear" button clears the grid.

Pressing the "save position" button save the current state of the puzzle, and pressing the "reload position" button reloads the last save position. Using these buttons is great for playing around with sudokus.

At the bottom of the screen you'll see a string of numbers which changes as you add or remove numbers from the grid. It is the whole game coded as a string of 81 numbers. You can save a copy of a game by copying and pasting this string into a file of your own. If you later copy and paste that string into the box and click the "set game" button, your saved game will reappear on the grid.

When you can see all the candidates, you can hide individual candidates in a cell by clicking on them. This will set them in a less visible colour. Clicking again will return them to their former colour. This is a useful feature when you are investigating intermediate and advanced techniques, which all involve reducing the number of candidates. Important: this will not help the "solve" process; only entering numbers in the grid will do that.

Have fun! Let me know what you think!