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How sudoku works

Sudoku is played on a 9 by 9 grid split into nine 3 by 3 boxes. A few cells start with numbers in them. Fill every empty cell so that each row, each column and each box holds the numbers 1 to 9 exactly once. That's the whole rule.

There's no arithmetic in it at all. The numbers could just as well be colors or letters, because the puzzle is only about where each one can and can't go. Every puzzle in Ninebark Sudoku has exactly one answer, and we check that each one can be reached with logic alone before you ever see it, so you never have to guess.

Five levels, sorted by technique

A lot of sudoku is graded by how many numbers are given at the start. We think that's a poor guide, since a sparse grid can be easy and a full one can be tough. Our solver works through each puzzle the way a person would and notes the hardest step it needed. That step sets the level.

Easy grids start with at least 36 numbers, so they move quickly. From Hard upward the grids are lean, usually 25 to 27 clues.

Hints that explain the next step

Tap Hint and we don't just drop a number in. We point to the cell, shade the row, column or box that matters, name the technique and explain it in a sentence or two. Tap Hint again and the number goes in. If a number you placed is wrong, the hint tells you that first, because nothing else will make sense until it's fixed.

There's no mistake limit, and Undo goes back as far as you like. If you'd rather have some pressure, the Three mistake challenge in Settings ends a puzzle after three wrong numbers.

The Daily Sudoku

Every day at midnight UTC there's a new Daily Sudoku, the same puzzle for everyone. The level follows a gentle week: Easy on Monday, Medium on Tuesday and Thursday, Hard on Wednesday, Friday and Sunday, and Expert on Saturday.

Your first solve of the day goes on the daily leaderboard, ranked by your time plus 30 seconds for each hint and 10 seconds for each wrong number. Solve on back to back days to build a streak, and tap any recent day on the calendar to play it again for fun.

Tips for your first puzzles

• Start with the number that's already on the grid the most. With six or seven placed, its last spots often fall out right away.
• Scan box by box. Asking where the 4 can go in this box is usually faster than asking what can go in this cell.
• Save notes for when the easy finds dry up. Then pencil in candidates one box at a time.
• Look for pairs. When two cells in a row can only be 3 and 8, every other cell in that row loses the 3 and the 8.

Our full Ninebark Sudoku guide goes through every technique, the keyboard controls and how the leaderboards score.

More puzzles like sudoku

If you like the feeling of a grid giving up its secrets one cell at a time, try Hedgehush, our minesweeper-style logic puzzle (our minesweeper online page explains it), or Mosaic Logic, where number clues on the rows and columns reveal a hidden picture. Cipher Cafe swaps numbers for letters with a daily cryptogram.

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