Sudoku: Fill the grid so every row, column and…

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Puzzle GamesSudoku

Zen Grid

Stage 1/ 30

Time

0:00

Mistakes

◇

Crystals

Score

Select a square and place a number.

81 empty

Select a square, then tap a number

Keyboard: 1–9 · Arrow keys to move · N for notes · Delete to erase

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About Sudoku

This build of Sudoku is a full 30 stage campaign, not a single difficulty picker. Stages are grouped into six five stage chapters, Gentle Focus, Quiet Patterns, Deep Thought, Master Logic, Zen Expert, and Grandmaster, and each stage generates its own puzzle on the spot: a solved grid is built by shuffling row bands, column bands, and the 1 to 9 digit set, then cells are deleted one at a time in random order, backtracking any removal that would leave more than one valid solution. That check runs on every cell removed, so every stage has exactly one correct answer even though nothing is drawn from a fixed puzzle bank. Clue count tightens as you climb: stage 1 leaves 46 of the 81 cells filled, and by the final chapter that drops to as few as 23. A pencil marks system sits behind the Pencil button or the N key: toggle note mode on, tap up to nine small numbers into any open cell, and the moment you place the true digit for that cell, matching pencil marks clear themselves automatically from every peer in its row, column, and 3x3 box. Selecting a cell highlights its row, column, and box plus every other cell already holding the same digit, and on mobile each number key disables itself once that digit has been placed nine times on the board. A hint reveals the correct digit for your selected cell, or a random unsolved one if nothing is selected, after a short pulsing highlight, the first one each stage is free and every one after that costs 20 crystals, crystals you earn by finishing stages. Wrong entries are not rejected, they go into the grid in red and add to a running mistake counter and a small score penalty, but nothing caps how many mistakes you can make or ends the run. A live per stage timer, a score built from plus 20 per correct entry and a stage completion bonus that scales with stage number, and a best time saved per stage all persist to the browser between sessions.

The parts of this build that matter for actually getting better at sudoku are the pencil marks and the hint economy, not the theme dressing. Real solvers rely on candidate marking to spot naked pairs, hidden singles, and pointing pairs before a cell's answer is obvious, and because placing a correct digit here wipes the matching pencil mark from every peer automatically, you get to practice noting candidates without the busywork of manually erasing them once a square is solved elsewhere, which is the habit that separates guessing from real deduction. The hint system is built to cost something: one free reveal per stage covers a genuine dead end, but every additional hint draws down the same crystal balance you need for later, harder stages, so leaning on hints early has a real opportunity cost. Because mistakes are tracked but never punished with a loss condition, you can test a candidate digit, see immediately from the red highlight whether it was wrong, and correct course, which rewards active hypothesis testing over frozen caution. And because the clue count drops gradually across 30 stages, the campaign itself functions as a difficulty ramp: the row, column, and box highlighting you lean on at 46 clues becomes a habit you still have once you are down to 23.

Jump into Sudoku at Playaby anytime — 100% free, browser-based, and zero downloads.

Our Take on Sudoku

What sold us wasn't the theme, it's that placing a correct digit automatically clears the matching pencil marks from every peer in its row, column, and box — that one detail removes the tedious housekeeping that makes candidate-marking annoying in most digital Sudoku. The hint system costs crystals after your first free one per stage, which gives leaning on hints a real opportunity cost instead of being free forever. Best for players who actually want to get better at deduction, not just clear a grid.

Best suited for: Solvers who want a real 30-stage campaign to work through over many sessions rather than one puzzle and done, and who like tools like pencil marks and row/column highlighting doing real work.

How to Play Sudoku

Objective

Fill the grid so every row, column and 3×3 box contains the digits 1–9 with no repeats.

Click a cell, then type or tap a number

Erase to clear a cell

Given clues are locked

Desktop Controls

Click a cell to select it, then press a number key 1-9 to fill it in
Press Backspace, Delete, or 0 to clear the selected cell
Given clue cells can be clicked to highlight their row/column but cannot be edited

Mobile Controls

Tap a cell to select it — this also highlights its row, column, and any matching digits already on the board
Tap a number on the on-screen 1-9 keypad below the grid to fill the selected cell
Tap "Clear" to erase the selected cell — no keyboard needed, the full keypad is always on screen

Tips for Sudoku

Turn on pencil marks, the Pencil button or the N key, before scanning a stage under 30 clues, since a wrong digit costs 10 points and stays on the board until you fix it yourself.

Selecting a cell highlights its row, column, box, and every cell already holding the same digit, use that highlight to check a candidate against every peer before typing it rather than guessing.

Save your free hint for a stage's last few empty cells instead of the first one you get stuck on, a late cell is more likely to be a genuine dead end than an early one you have not scanned carefully.

Crystals only come from finishing stages, 3 to 15 depending on the chapter, and any hint after the first costs a flat 20, so spending them early in an easy chapter leaves fewer for the 23 clue stages near the end.

A wrong digit stays on the board in red until you overwrite it, since there is no mistake cap, treat a red cell as an instant signal to fix now rather than something to sort out later.

Placing a correct digit automatically wipes that same number's pencil marks from every peer in its row, column, and box, so mark candidates generously and let the cleanup happen on its own.

On mobile, a number key disables itself once that digit has been placed nine times, use that as a fast check for which digits are already fully placed without counting manually.

Sudoku — Frequently Asked Questions

How do you play Sudoku?

Fill the grid so every row, column and 3×3 box contains the digits 1–9 with no repeats. Click a cell, then type or tap a number.

Is Sudoku free to play?

Yes — Sudoku is completely free to play on Playaby, with no downloads, no account, and no in-game purchases.

Can I play Sudoku on my phone or tablet?

Yes. Sudoku runs directly in your browser, so it works on desktop, phone, and tablet with touch controls built in — there's nothing to install and no extra permissions needed.

What are the controls for Sudoku?

Click a cell, then type or tap a number. Erase to clear a cell. Given clues are locked.

Where can I find more puzzle games like Sudoku?

Playaby has a full page of free puzzle games you can browse and jump straight into — no downloads required for any of them.

Is there a notes or pencil marks mode in this Sudoku?

Yes. Tap the Pencil button on mobile or press N to toggle note mode, then tap up to nine small numbers into any open cell as candidates. Placing the actual correct digit in a cell automatically clears that same digit's pencil marks from every cell sharing its row, column, and 3x3 box, so you are not stuck manually erasing outdated notes.

What sudoku solving techniques should I practice to get better in this build?

Lean on the peer highlighting the game already gives you: selecting a cell lights up its full row, column, box, and every cell sharing its digit, which is the same information a naked single or hidden single scan relies on. Note every candidate in a tight cell before committing, then watch which candidates disappear as peers fill in, since that is how a real solver narrows a cell to one answer instead of guessing.

How do the difficulty tiers differ in this Sudoku?

Difficulty is set by how many of the 81 cells stay filled in at the start of a stage, and it is tied directly to your stage number rather than a menu choice. Stage 1 leaves 46 clues, the count tightens roughly one clue at a time through each five stage chapter, and by the final Grandmaster chapter as few as 23 clues remain.

Does making mistakes end the game or cost me progress?

No. A wrong digit turns red, adds one to the mistake counter shown at the top of the board, and costs 10 points, but there is no mistake limit and no fail state, you can correct it as many times as you need until the stage is solved.

How do hints work, and what do they cost?

The first hint on any stage is free. After that, each hint costs 20 crystals, the same currency you earn, 3 to 15 depending on the stage's chapter, for completing a stage. A hint reveals the correct digit for your currently selected cell if it is still unsolved, or a random unsolved cell if not, after a brief pulsing highlight.

Can I play this Sudoku with just a keyboard?

Yes, and on desktop that is effectively the intended input: number keys 1 to 9 fill the selected cell, Backspace, Delete, or 0 clear it, arrow keys move your selection, and N toggles pencil mode. The on-screen number pad only appears on mobile layouts.

Are the puzzles guaranteed to have only one solution?

Yes. Each puzzle is generated by solving a fresh 9x9 grid, then removing cells one at a time in random order, and a backtracking solution counter checks after every removal that exactly one solution still exists. A cell is only left blank if removing it does not create a second valid solution.

Stage 1/ 30

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About Sudoku

Our Take on Sudoku

Difficulty

How to Play Sudoku

Playing on Mobile

Tips for Sudoku

Sudoku — Frequently Asked Questions

Learn More About Sudoku

Every Type in Sudoku (6)

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