---
title: "Hard sudoku online, free: a puzzle with no guessing"
description: "Hard sudoku online for free, instant in your browser. A new puzzle every time, one solution and the techniques this level really needs."
url: https://games.klyo.pl/hard-sudoku/
canonical: https://games.klyo.pl/hard-sudoku/
type: strona
language: en
author: klyo
organization: Klyo Illia Krasnopolskyi (NIP 7822656871), Łódź, Poland
contact: kontakt@klyo.pl
updated: 2026-11-05
llms: https://games.klyo.pl/llms.txt
---

# *Hard* sudoku online

This page opens a new puzzle at Hard level right away. About 29 given digits, one solution and no guessing, free in a browser on phone or computer.

![Sudoku: browser game by Klyo](https://games.klyo.pl/foto/zrzut-gra-sudoku-2-1200.76f245f6.jpg)

Play hard sudoku

The game runs right here. Nothing to install, no account needed.

[JavaScript is turned off in your browser. Open Sudoku in a new tab.](https://g-sudoku-2.klyo.pl/?poziom=hard)

Sudoku

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## What makes this puzzle hard

The number of digits alone does not decide the difficulty here. The generator checks every puzzle and only rates it Hard when it truly needs pairs and pointing cells. Spotting missing digits will not get you to the end. So a hard puzzle will not turn out to be an easy one in disguise, and yet every one can be solved by logic, without a single guess.

## The techniques you need

Start with notes: pencil in the candidates in every empty cell, because you will not see pairs without them. A pair is two cells in one row, column or box holding the same two digits, for example 3 and 8. You can then remove those digits from the other cells of that group. Pointing cells work in a similar way: when a digit can only sit in one row within a box, it goes from the rest of that row. After every removal, check single cells again, because new ones often appear.

## The rules of this game

You have three hints, and three mistakes end the game. A mistake costs 120 points and the score pool shrinks every second, so pace counts too. An interrupted game waits under Continue, and this link will not erase a game you have already started. A hint does not fill in a digit right away, it shows the simplest logical step. When Hard stops being a challenge, Expert, Master and Extreme are waiting above it.

## How to start a hard puzzle

Do not fill in notes straight away. Go through the digits first, starting with the most frequent one, and check where it can stand in each box. That fills the first cells quickly and cheaply. When those moves run out, turn on notes and add candidates across the whole board. Look for pairs in boxes first, because they are easiest to see, then in rows and columns. If you get stuck, do not guess: a mistake costs points, and a hint shows you the technique you are missing.

## Other sudoku levels

All six levels, from Easy to Extreme, and the daily sudoku are on the main game page.

[Sudoku](https://games.klyo.pl/sudoku/)

---

Source: https://games.klyo.pl/hard-sudoku/ · Built and run by klyo, a Polish technology company (Łódź) · Contact: kontakt@klyo.pl · Index for language models: https://games.klyo.pl/llms.txt