How to play

The rules

A sudoku grid has 81 cells, arranged in 9 rows, 9 columns and 9 boxes of 3 by 3 cells. Some cells are filled in when you start. Your job is to fill the rest so that every row, every column and every box contains the digits 1 to 9 exactly once.

That is all. There is no maths, and you never need to guess. Every puzzle on sudoku.ie has exactly one solution, and you can always reach it by reasoning. If you are new to sudoku, our guide to the basics walks you through your first moves.

Entering digits

Tap a cell to select it, then tap a number to place it. To change a digit, select the cell and tap a different number.

The givens (the digits that were there at the start) are fixed, and you cannot change them.

Notes mode

Notes let you jot down the digits that could still go in a cell. Turn on notes mode with the pencil button, then tap a cell and the digits you want to note. They appear small inside the cell. Tap a digit again to remove it. Turn notes mode off to go back to placing digits.

Keep your notes up to date as you place digits, and they will point you to the next move. Our guide to pencil marks explains how to get the most out of them.

Undo and erase

Undo steps back one move at a time, as far as you like. Erase clears the selected cell, whether it holds a digit or notes.

Hints that teach

Stuck? The hint button does not just fill in a cell. It finds the next logical step, highlights the cells involved, and explains the reasoning in plain English, naming the technique used. Each technique has its own guide in our Learn section. Using a hint is a good way to pick up a new technique.

Digit counts

Each number button shows how many of that digit are still to be placed, so you can see at a glance which digits are nearly done. A digit with only one or two left to place is often a quick win.

The daily puzzle

There is one daily puzzle for everyone in Ireland. It changes at midnight Irish time, and everyone gets the same grid, so you can compare times with friends, family or the office.

The difficulty follows the week:

• Monday: Easy
• Tuesday and Wednesday: Medium
• Thursday and Friday: Hard
• Saturday: Expert
• Sunday: Medium

So the week starts gently, builds to a challenge on Saturday, and eases off for Sunday. When you finish, your time goes on the daily leaderboard. Missed a day? Past puzzles are in the archive.

Printing

Prefer pen and paper? Use the print button on any puzzle for a clean copy. Our printables page has large-print puzzles, several puzzles per page and a full week’s booklet.

Playing offline

Once the page has loaded, you can keep playing even if your connection drops, which is handy on the train or in a spot with poor signal. Your progress, stats and streaks are kept in your browser.

Frequently asked questions

Do I need an account?

No. You can play every puzzle without signing up. Your progress, stats and streaks are kept in your browser on the device you play on.

What happens if I make a mistake?

Nothing dramatic. Use undo to step back one move at a time, as far as you need, or erase to clear a single cell. If you are not sure where things went wrong, a hint will show you a sound next step.

Do I ever need to guess?

Never. Every puzzle has exactly one solution and can be solved with logic alone. If you feel stuck, our guide to getting unstuck has a routine that helps, and the hint button will show you the next step.

How is difficulty decided?

Each puzzle is graded by the hardest technique needed to solve it. Easy puzzles need only singles. Medium adds pointing, claiming and pairs. Hard adds triples, quads and the X-wing. Expert adds the XY-wing, XYZ-wing and swordfish.

When does the new puzzle appear?

At midnight Irish time, every day. That is midnight in Dublin, whatever the season.

Will I lose my streak if I play on a different device?

Your streak and stats are stored in the browser you play on. If you switch to a different phone, computer or browser, it starts fresh there unless you copy it across with the link on your stats page. Clearing your browser data will also reset them.

Can I play old puzzles?

Yes. The archive has every past daily puzzle, so you can catch up on days you missed or try a Saturday Expert again.

Is sudoku.ie suitable for children?

The daily puzzles suit older children who enjoy a challenge. For younger children, our kids’ page has smaller 4 by 4 and 6 by 6 grids, which are a lovely way to start.