Sudoku

This is a free online Sudoku with an endless supply of freshly generated puzzles at four difficulties, from Easy to Expert. It runs in your browser on desktop and mobile, with no sign-up.

How to play

Fill the 9 by 9 grid so that every row, every column and every 3 by 3 box contains each digit from 1 to 9 exactly once. Some cells are filled in to start with, and every puzzle has exactly one solution.

• Mouse or touch: select a cell, then tap a digit on the number pad. Erase clears the cell, Undo takes back your last move, and Hint fills in one cell for you, the selected one if it is empty or wrong, and lowers your score.
• Keyboard: arrow keys move between cells, 1 to 9 place a digit, Backspace, Delete or 0 clear a cell, N toggles Notes, and Ctrl+Z undoes.
• Mistakes are counted as you play, and the game tells you how long you took when you finish.

History

The timeless number-placement puzzle, built from scratch for Hybrid By Nature.
Every puzzle is generated on the fly with a guaranteed unique solution — no
two games are ever the same.

Usage Tips

• Tap a filled cell to highlight every matching number on the board.
• The number pad shows how many of each digit are still left to place.
• Toggle Notes (or press N) to jot pencil marks; placing a digit
  automatically cleans up notes in the same row, column, and box.
• Switch to Colours mode from the menu to swap the nine digits for
  nine colourblind-safe hues — keyboard 1–9 still places them in order.
• Flip on Show symbols to draw a distinct shape inside every colour
  swatch, so colour alone is never the only way to tell them apart.
• Every solve is scored on time, mistakes, and hints used. Open
  Top scores from the menu to see your best five runs per
  difficulty, tracked separately for numbers and colours.
• Your game saves automatically — close the tab and resume any time.
• Install it as an app on your phone for offline play.

Technical Notes

• Puzzles are generated with randomized backtracking, then clues are removed
  while a counting solver verifies the solution stays unique.
• Difficulty controls how many clues remain (about 40 down to 25).
• Score is base points per difficulty (1000–5000), scaled by how your
  time compares to a par time, then reduced for mistakes and hints used.

Questions

Is it free? Yes. There is nothing to buy and no account to make.

Does it save my game? Yes. Your puzzle autosaves in your browser, so you can close the tab and resume from the menu.

Are the puzzles always solvable by logic? Every puzzle has a single solution, checked when it is generated.