Stuck? See How To Solve Sudoku!

How to play
First, create a new puzzle. You can do this by pressing 'Random Puzzle' or 'Seed Puzzle', or you can type the starting numbers in from another puzzle, e.g. one from a book or newspaper. Follow the instructions in the right-hand column for typing in your own numbers.

To solve the puzzle, type numbers into the empty squares so that each horizontal row and vertical column contains the numbers 1 to 9 (i.e. with no numbers repeated). The difficult bit is that each 9-square rectangle (the areas surrounded by darker lines) must also contain the numbers 1 to 9, with no repetitions. To see an example of a completed puzzle, press 'Solve Puzzle'. 

Tip - you can press 'Check my answer' after each number you type in. It'll tell you whether your answers so far are correct, without revealing the rest of the puzzle. For some good tips on how to solve sudoku puzzles, see the 'How to solve' section at www.sudoku.com.

Basic tips for solving have now been moved to the new (and expanded) How to solve page!

Using number hints. A key technique in sudkou solving is writing the candidate numbers for each square in the corner of the square - this helps you to recognise patterns such as pairs (see above). You can do this in this page, by clicking in the top-left corner and typing the numbers in.

In manual mode it's up to you to maintain these lists, just like a printed puzzle. In automatic mode, the page calculates the lists for you, updating them whenever you change a square's number. That's not 'proper' solving, of course, but is useful for practising pattern recognition.

Generating puzzles.
This page features the all-new MKII puzzle generator, which actually works a bit like the serious ones (i.e. it doesn't depend on the 'infinite monkeys' theory of random content generation). It's still 'random' though, in that it uses random numbers to fill the starting squares.

Puzzles generated by the 'Random Puzzle' button have just one solution, and a symmetrical layout. You can choose between 36, 30 or 26 starting squares. The difficulty rating of a puzzle is unknown until it's been generated, but choosing fewer squares will tend  to create harder puzzles.

The 'Quick puzzle' button generates a single-solution puzzle with between 29 and 36 starting numbers, in a non-symmetrical layout (some people consider non-symmetrical puzzles not 'proper' sudoku, while others think they're a bit of a walk on the wild side!). Quick puzzles are almost all rated 'easy'.

If you type your own puzzle in, or import it via the Import/Export button, then you can find out if it has more than one solution by clicking 'Check'. 

To be solvable entirely by logic (no guesses), a puzzle must have only one possible solution.

Have fun!


 

Tip: Use Firefox to view the solver - it shows the numbers as they're being calculated.

Tip #2: If you're using number hints, press Tab after you type each number - this will update the tips for other cells.

Tip #3: When importing and solving really tough puzzles, your browser may show 'Script running slowly' messages. Choose 'No' (IE) or 'Cancel' (Firefox) to let the solver keep on running. It'll get there in the end!

Links:
Sudoku.com. The 'official' sudoku site - puzzles, tips, links.

The Daily Sudoku. A new puzzle every day, plus lots of links.

Daily Telegraph Sudoku. Puzzles and links, plus an excellent guide to solving techniques.

Sudoku Solver. This Excel-based solver gave me the idea for the solver in this page - thanks!

Mark Huckvale's Sudoku Workpad. Puzzle generator and solver, and the inspiration for the Seed Puzzle generator on this page.

How the solver in this page works for anyone who's interested.