Sudoku
Logic-only puzzles in five levels, plus a new puzzle every day
Free browser Sudoku with five technique-graded levels, a daily puzzle with streaks, and hints that name the solving technique. Every puzzle is solvable without guessing.
Features
Never a guess
Each puzzle has exactly one solution, and our solver confirms it can be reached by logic alone.
Hints that teach
A hint points to where to look and names the technique, from hidden singles to X-Wing.
Daily challenge
One shared puzzle a day, easier early in the week, with a streak for puzzles solved on the day.
Notes and auto notes
Pencil in candidates by hand or all at once; placing a number clears it from its row, column and box.
How it works
- 1
Choose a level or today's puzzle
Pick from Easy to Evil, or open the daily challenge that everyone plays.
- 2
Fill the grid
Select a cell and enter a number from 1 to 9 with the pad or keyboard, using notes as needed.
- 3
Complete every unit
The puzzle is solved when every row, column and 3 × 3 box holds each number exactly once.
About the game
Sudoku is played on a 9 × 9 grid split into nine 3 × 3 boxes. Some numbers are given, and the goal is to fill every empty cell so that each row, column and box contains the numbers 1 to 9 exactly once. Seriauth’s version is built around one rule: no puzzle should ever require guessing.
It suits people who want a calm daily habit as well as experienced solvers looking for harder techniques.
What we built
We wrote our own puzzle generator and a solver that works the way a person does, applying named techniques one step at a time. Every puzzle is checked for a unique solution, and its level is set by the hardest technique the solver needed rather than by how many numbers are given. That gives five levels: Easy, Medium, Hard, Expert and Evil, where Evil calls for Swordfish or XYZ-Wing.
The same solver powers the hints. Instead of filling in an answer, a hint shows where to look and names the technique that applies. The daily challenge is the same puzzle for everyone, easier on Monday and hardest at the weekend, with a calendar of past days and a streak counter.
The game also has undo, auto-save, a pause key, light and dark themes, and local statistics. A seven-part beginner guide, illustrated with screenshots of real puzzles, walks from the first game through X-Wing and the wing techniques. The interface is available in 11 languages.
FAQ
How are the difficulty levels decided?
By the hardest technique a puzzle needs. Easy and Medium use singles, Hard adds pairs, Expert adds triples and X-Wing, and Evil adds Swordfish.
When does the daily puzzle change?
At midnight in your own time zone. Past days can be played from the calendar, but only puzzles solved on the day count toward your streak.
Where are my stats stored?
Games played, win rate, best and average times and streaks are saved in your browser only.
Can I play with a keyboard?
Yes. Arrow keys move, 1 to 9 fill a cell, N or Shift with a number adds notes, Ctrl+Z undoes and H asks for a hint.
More from this series
View all work
Let's turn a good idea into something real
Partnerships, product questions or suggestions — we'd love to hear from you.