🔢 Sudoku Online

Four difficulty levels plus a daily puzzle, with pencil notes and smart highlights - practice right in your browser

👥 1 player🎲 Board & Puzzle⚡ No download · No sign-up

🧩 Sudoku

Choose a difficulty

Records are saved only in your browser, never uploaded

🕹️ How to play

Pick a difficulty or the daily puzzle: Tap easy/medium/hard/expert, or tap the daily puzzle to play the same board as everyone else that day. A 9×9 puzzle with a guaranteed unique solution is generated instantly and the timer starts.
Select a cell and enter a digit: Tap an empty cell then a 1–9 key to place a digit; the selected cell highlights its row, column, box and matching digits to help you eliminate. Given clues are bold and cannot be changed.
Use pencil notes for candidates: When unsure, toggle Notes and press digits to jot small candidates in a cell (add/remove freely); use Erase to clear a cell, Undo to step back, and Hint to reveal one correct digit if stuck.
Fill the board and see your time: Fill the whole 9×9 correctly to win; your time shows against the difficulty's best, records trigger a celebration, and a clean solve (0 mistakes, 0 hints) earns a badge. Play again or switch difficulty.

📖 Rules & variants

Basic rules: the 9×9 board is split into nine 3×3 boxes with some cells pre-filled (givens, not editable). Fill the empty cells with 1–9 so each row, column and 3×3 box contains 1–9 exactly once with no repeats. Complete it to win.

Unique solution: every board is generated by backtracking a full solution then digging cells while a solver verifies uniqueness (stopping at a second solution), so there is exactly one answer — no multi-solution or unsolvable puzzles, letting you reason instead of guess.

Four difficulties: easy to expert differ mainly by how many cells are given — fewer givens means more reasoning steps and higher difficulty. Difficulty is an approximate casual grading, not a strict technique-tier rating.

Notes, hints and mistakes: notes mark small candidates in a cell and can auto-clear from related cells after you place a digit; with auto-check on, a digit that differs from the solution turns red and counts a mistake. An optional 3-mistake fail mode is off by default. Wins using hints or with mistakes don't count toward the clean best time.

Scores and daily puzzle: time is the core score, and each difficulty's best time only records clean solves (0 hints, 0 mistakes). The daily puzzle is generated deterministically from the date so everyone plays the same board, with a check-in streak. Progress, best times and check-ins live only in your browser, auto-resuming on refresh, no login needed.

❓ FAQ

How do you play sudoku?

Fill a 9×9 grid with 1–9 so every row, column and 3×3 box has each digit once with no repeats. Start where rows, columns or boxes already have many numbers, use elimination to find a cell's only possible digit, and keep going until the board is full and correct.

What are some sudoku tips for beginners?

The most useful are the naked single and box elimination: check whether a cell has only one possible digit after ruling out its row/column/box, or whether a digit fits only one spot in a box. Start on easy, use notes to track candidates, and see the sudoku strategy guide for more.

Does sudoku always have a unique solution?

A proper sudoku has exactly one solution — that is what makes pure logic possible. This site verifies uniqueness while generating each board and refills any cell that would allow a second solution, so you never get a multi-solution or unsolvable puzzle.

How do sudoku pencil notes (candidates) work?

Toggle Notes and press digits to jot small candidates in a cell, so you can list all possibilities before narrowing down. Switch back to normal mode to place the final digit; with auto-clear on, placing a digit removes it from related cells' notes automatically.

How is sudoku difficulty decided? Easy vs expert?

The four levels differ mainly by how many cells are given: easy has the most and almost fills itself, expert has the fewest and needs heavy elimination and candidate reasoning. Fewer givens mean fewer clues and longer chains, so higher difficulty; it's an approximate casual grading.

How long should a sudoku take? What's a good time?

As a rough guide, most people finish easy in 3–8 minutes and medium in 6–15, while hard and expert often take tens of minutes; experienced players go much faster. Times depend heavily on difficulty, practice and note use, so ratings here are just for fun.

🎮 Related games

⚠️ Every puzzle here is generated on the fly and verified to have a unique solution; it is for casual play, and time ratings are for fun, not a competitive standard.

Last updated: 2026-07-20 · Saved on this device only