This sudoku online game makes every grid with our own generator and lets the sudoku solver check it: one answer only, and a rating from the hardest technique its human-style logic uses. Pick a level and play a fresh grid, or the puzzle of the day that everyone gets.
Sudoku rules in short
Fill the 9 by 9 grid so that each row, each column and each of the nine 3 by 3 boxes contains the digits 1 to 9 exactly once. The black digits are given and cannot change; yours appear in blue. When a digit clashes with another one in its row, column or box it turns red straight away.
Select a square and tap a digit, or type it. Pencil switches to candidate mode, where digits go in small; placing a real digit clears that digit from the candidates around it. Squares in the same row, column and box are shaded, and every copy of the selected digit is highlighted, which makes scanning quicker.
How the levels are measured
- Easy keeps 36 given digits and needs nothing beyond singles: a digit that fits in only one square of a house, or a square with only one digit left.
- Medium grids have the fewest clues the generator could leave and need at least one Medium step, such as a pointing pair or a naked pair, but nothing harder.
- Hard grids need Hard or Expert techniques such as triples, X-wings, swordfish or XY-wings, and never trial and error.
The sudoku techniques page explains each of these with an example, and X-wing sudoku covers the fish pattern in depth.
Tips for faster solving
- Start with the digit that already appears most often and look for the box where it is still missing.
- Finish nearly full rows, columns and boxes first: one gap means a full house.
- On medium and hard grids, pencil in candidates for a box at a time rather than the whole grid at once.
- When you are stuck, look for two squares in a house that share the same two candidates: those digits are taken there.
Hints, mistakes and stats
Hint gives the step the solver would take next, with its reason and the squares involved, and fixes a wrong digit first if there is one. Steps that only remove candidates update your pencil marks. Check marks digits that disagree with the answer, and Show mistakes keeps that on. Games, best and average times, and your daily streak are stored per level on this device. For a step-by-step method from zero, read how to solve sudoku. Want a twist? Try killer sudoku or sudoku X.
Solver tested . Found a problem? Tell us.
Questions
How many clues does a sudoku need?
At least 17 for a classic 9 by 9 grid to have a single answer; that was proven by an exhaustive computer search. Our medium and hard grids remove clues until no more can go without allowing a second answer.
Is a puzzle with fewer clues always harder?
No. Difficulty depends on the techniques needed, not on the clue count. That is why levels here are set by the rating from our solver.
What do the blue and red digits mean?
Blue digits are yours. A digit turns red when it repeats in its row, column or box. Check and Show mistakes also mark digits that break no rule yet but disagree with the answer.
Is the puzzle of the day the same for everyone?
Yes. Our generator builds it from the date, one grid per level, and it changes at midnight on your device.
Can I play on my phone?
Yes. Tap a square and use the number pad under the grid. Everything runs in your browser; nothing is sent anywhere.