About This Free Online Sudoku
This is a complete, self-contained game of Sudoku that runs right in your browser. The classic logic puzzle asks you to fill a 9×9 grid so that every row, every column, and each of the nine 3×3 boxes contains the digits 1 through 9 with no repeats. Tooldit generates a brand-new, solvable board every time you start a game, tracks your time and mistakes, and saves your progress automatically — so you never lose a puzzle halfway through. There is nothing to install and nothing to configure; the whole game is built and solved on your own device.
How to Play
The goal is simple to state and satisfying to reach: place a digit in every empty square so the 1–9 rule holds across every row, column, and box. Here is what each control does:
- Pick a difficulty — choose Easy (40 starting clues), Medium (32), or Hard (26). Picking a level immediately deals a fresh board, and each card shows your best time for that level.
- Select a cell — tap any empty square. The game highlights its row, column, and box, plus any cells sharing the same number, so conflicts are easy to spot.
- Enter a number — tap the on-screen number pad, or on a keyboard press 1–9. Use arrow keys to move between cells and Backspace, Delete, or 0 to clear one.
- Notes mode — toggle it on (or press N) to add small pencil-mark candidates to an empty cell instead of a final answer. Tap a digit again to remove that note.
- Check, Hint, and Clear — Check briefly flags any wrong entries, Hint reveals one correct cell (three per game), and Clear empties the selected cell.
A live timer, a mistake counter, and a hint counter sit above the board. There is no score to chase — the challenge is to solve the grid as fast as you can with as few mistakes and hints as possible. Solve the whole board correctly and a victory card shows your finishing time, and a new personal best is recorded for that difficulty.
Tips and Strategy
- Scan for the obvious first. Look for rows, columns, or boxes that are nearly full — a square with only one possible digit (a "naked single") is the safest move you can make.
- Hunt one number at a time. Pick a digit, then check each box to see where it can legally go. Often a number has exactly one home in a box, even if that cell isn't otherwise constrained.
- Lean on notes for the hard parts. On Medium and Hard boards, pencil in candidates before committing. When a cell's note list shrinks to one number, you've found your answer without guessing.
- Keep "Show mistakes" on while learning. Wrong entries turn red instantly, which teaches the rules fast. Turn it off later for a stricter, more authentic challenge.
- Save hints for genuine dead ends. Because you only get three, spend them when you're stuck rather than to speed through — your end-of-game summary counts them.
Why People Love Sudoku
Sudoku is pure deduction — no math beyond counting, no vocabulary, no luck. That makes it a great mental warm-up, a quiet break between meetings, or a screen-friendly way to relax without the noise of a typical mobile game. A US commuter can knock out an Easy grid on the train, a student can sharpen their pattern recognition between study sessions, a parent can hand a tablet to a kid for a clean, ad-free puzzle, and a longtime solver can fight for a faster best time on Hard. Because everything runs locally and your board is remembered, it fits naturally into the gaps in a busy day.
Looking for another quick brain break? Try our 2048 number puzzle, the word-building Word Puzzle, or browse all Tooldit games.
Frequently Asked Questions
+Is this Sudoku game free to play?
Yes. Every puzzle, every difficulty, and the timer, hints, and notes features are completely free. There is no sign-up, no account, no payment, and no ads inside the grid. Just open the page and start solving.
+How many difficulty levels are there and how do they differ?
There are three: Easy, Medium, and Hard. Each level changes how many starting numbers (clues) you get. Easy gives you 40 clues, Medium gives 32, and Hard gives only 26. Fewer clues means more cells to deduce and harder logic chains.
+What are notes and when should I use them?
Notes (also called pencil marks) let you jot small candidate numbers into an empty cell instead of committing to a final answer. Turn on Notes mode, then tap digits to add or remove them. Use notes on tougher cells where two or three numbers are still possible so you can track candidates without guessing.
+Do hints give away the answer?
A hint fills in the correct number for one cell, and you get up to three per puzzle. It targets the cell you have selected if that cell is wrong or empty; otherwise it finds the first unsolved cell for you. Hints are counted in your end-of-game summary, so they are best saved for when you are truly stuck.
+Will I lose my progress if I close the tab?
No. Your current board, difficulty, timer, mistake count, and best times are saved automatically in your browser's local storage. Come back later on the same device and browser and the puzzle is exactly where you left it. Nothing is sent to a server.
+Does the game work on a phone and offline?
Yes to both. The grid scales to fit small screens, and you tap a cell then tap the on-screen number pad to play. Because puzzles are generated and solved entirely in your browser, the game keeps working once the page has loaded even if your connection drops.