Sudoku: Classic Number Puzzle

Sudoku, with two things most sudoku apps get wrong put right: the difficulty
label means something, and the hints teach you something.

Fill the grid so every row, column and three-by-three box holds 1 to 9 once
each. Tap a square, tap a number. That is the whole game.

THE DIFFICULTY IS MEASURED, NOT GUESSED

Most sudoku apps set difficulty by counting the clues they removed, which is a
famously bad measure. Every puzzle here was solved the way a person solves one,
one named technique at a time, and its difficulty is the hardest technique it
actually needed.

Easy Scanning only, and plenty of clues to scan.
Medium The same reasoning, with much less to go on.
Hard Needs you to spot where a digit cannot go, not just where it can.
Expert Needs pairs, triples and patterns across two units at once.

NO GUESSING, EVER

A sudoku with more than one answer is a trap: you fill a grid that breaks no
rule and the game says you are wrong. Every board here was checked twice before
it shipped, once for exactly one answer and once to confirm pure logic can
finish it with no guess anywhere.

HINTS THAT EXPLAIN, NOT HINTS THAT ANSWER

"The answer is 7" teaches you nothing and trains you to press the button again.
Every hint here gives the reason first:

"In box 2 every remaining 5 sits in the same column, so no other square in
that column can be a 5."

Read the reason and go back to the grid, or take the digit. The first hint on
every puzzle is free.

NEVER PLAYED BEFORE? START HERE

A guided first puzzle walks you through a whole board, one rule at a time,
naming each rule at the moment you need it. It is on the home screen, and it
stays in the settings menu afterwards.

650 PUZZLES, AND A NEW ONE EVERY DAY

200 easy, 200 medium, 150 hard and 100 expert, all included and playable
offline. Plus a daily puzzle -- the same board for everybody -- with a streak
you can see, and an advert to bring a lapsed one back if you miss a day.

EVERYTHING THAT MAKES A SUDOKU PLEASANT

Pencil marks, free and unlimited, with an optional one-tap fill.
Placing a digit clears it from the marks of every square that can see it.
Unlimited undo, and erase any square at any time.
Tap a number on the keypad to light up every place it sits AND every square
you have pencilled it into, each one ringed.
The row, column and box you are working in are highlighted too.
Duplicates show up as you type them.
A timer you can ignore, and your fastest time at each difficulty.
A quiet music bed with its own switch, so turning it off keeps the sounds
that tell you what the board just did.

EARN PENCILS, SPEND THEM ON LOOKS ONLY

Every puzzle pays pencils -- more for a harder board, and more for a board you
finished with no mistakes. Collect a daily handful that grows the longer your
run lasts, and buy a lapsed streak back with an advert if you miss a day.

Pencils buy your pencil colour, the paper the grid is printed on, and the
colour that lights up matching numbers. That is the whole shop: nothing that
makes a puzzle easier, no hints for sale, no extra lives, and nothing that
costs real money.

ADVERTS YOU CHOOSE, AND NEVER ANY OTHER KIND

No banners. Nothing between puzzles. Nothing that starts on its own. Every
advert here is a button you decided to press, it says AD first, and it names
what it gives you -- a hint, a square, a check of your grid, or double the
pencils you have already been paid.

Declining costs you nothing. The plain reward is always collected by the free
button beside the offer.

THREE MISTAKES, AND A WAY OUT THAT IS ALWAYS FREE

Three wrong digits stop the puzzle. From there, watch an advert to keep the
grid you have filled in, or start the same puzzle again: free, always, no
advert involved. The advert buys your own work back, not the ability to finish.

No energy. No lives to wait for.

Works completely offline. No account, no sign-in, nothing to join.