Hoot's Puzzles

Hard puzzles for a maths brain, in a cosy little town. Seventeen kinds of sudoku plus Calcudoku, Kakuro, Skyscrapers, Sum Skyscrapers, Futoshiki, Renzoku, Suguru, Ripple Effect, Straights and Inshi no Heya, each with four difficulty ranks and a 30-puzzle collection. There are 99,999 puzzles per rank, and each has its own number, so you can replay one or share it with a friend. Every puzzle has exactly one solution, reachable by logic alone, and Professor Hoot is on hand with hints.

Daily puzzle

Today's Chimera

Two or three rule systems at once, at Theorem rank. The same puzzle for everyone today.

Rank

Puzzle № (1–99,999)

Sudoku

More number puzzles

How to play

Hoot’s Puzzles has seventeen kinds of sudoku and ten other number puzzles, all free. Here are the rules for each, with a tip from Professor Hoot to get you started.

Classic Sudoku

Place 1–9 once in every row, column and 3×3 box.

Tip: Start with hidden singles: pick a box and ask where each missing digit could go. Often only one cell is left.

Killer Sudoku

No digits are given. The digits in each dashed cage add up to its total and never repeat within the cage.

Tip: Learn the small cage combinations: 3 in two cells is always 1 and 2, and 17 in two cells is always 8 and 9. Every row, column and box adds up to 45.

Thermometer Sudoku

Digits strictly increase along each thermometer, starting from the bulb.

Tip: A thermometer of n cells limits its bulb to at most 10−n and its tip to at least n.

Arrow Sudoku

The digits along an arrow add up to the digit in its circle. Digits may repeat on an arrow if the other rules allow.

Tip: A two-cell arrow adds to at least 3, so its circle can never be 1 or 2.

Kropki Sudoku

A white dot joins consecutive digits; a black dot joins two digits where one is double the other. Every possible dot is shown.

Tip: A black-dot pair is 1-2, 2-4, 3-6 or 4-8, so neither cell can be 5, 7 or 9. Because every dot is shown, neighbours without a dot are neither consecutive nor doubles.

XV Sudoku

An X joins two digits that add to 10; a V joins two that add to 5. Every possible X and V is shown.

Tip: A cell on an X can never be 5, and a V pair is always 1-4 or 2-3.

Sandwich Sudoku

A clue outside the grid is the sum of the digits between the 1 and the 9 in that row or column.

Tip: A clue of 0 means the 1 and 9 are side by side; a clue of 35 means they sit at the two ends.

German Whispers

Neighbouring digits along a green line differ by at least 5.

Tip: A 5 can never sit on a green line, and the digits along a line alternate between low (1–4) and high (6–9).

Sudoku X

Both main diagonals also contain 1–9 once.

Tip: Treat each diagonal as an extra house and look for hidden singles along it.

Anti-Knight Sudoku

Two cells a chess knight’s move apart can never hold the same digit.

Tip: Each placed digit rules out up to eight extra cells, often in the neighbouring boxes.

Renban Sudoku

Each purple line holds a set of consecutive digits, in any order, with no repeats.

Tip: A line of five or more cells always contains a 5.

Palindrome Sudoku

Each grey line reads the same from either end.

Tip: Mirror-image cells hold the same digit, so they can never share a row, column or box.

Between Lines Sudoku

Along each line with a circle at both ends, every digit lies strictly between the two circled digits.

Tip: The two circles can never be consecutive digits, because something has to fit strictly between them.

Little Killer Sudoku

A clue outside the grid is the sum of the digits along the diagonal its arrow points to. Digits may repeat on a diagonal.

Tip: Short diagonals with very small or very large totals are the easiest place to start.

Windoku

Each of the four shaded 3×3 windows also contains 1–9 once.

Tip: The windows overlap the normal boxes, so a digit pinned in a window often settles a box as well.

Non-Consecutive Sudoku

Cells that share an edge never hold consecutive digits.

Tip: Next to a 5, a cell can be neither 4 nor 6. Placed digits remove their neighbours’ values from the cells beside them.

Chimera Sudoku

Two or three of the rule sets above, layered into one puzzle. A new daily Chimera appears every day.

Tip: Look for the rule that constrains the most cells and start there.

Calcudoku

Place 1 to N once in every row and column of an N×N grid. The digits in each cage combine to its target with the operation shown (+, −, × or ÷). Digits may repeat in a cage if they are in different rows and columns.

Tip: Factorise multiplication cages first: in a 6×6, 15× over two cells can only be 3 and 5.

Kakuro

Fill each white cell with 1–9. Every run of white cells adds up to its clue, with no digit repeated in a run.

Tip: Some totals have only one combination: 16 in two cells is always 7 and 9, and 24 in three cells is always 7, 8 and 9.

Skyscrapers

Place towers of height 1 to N once in every row and column. A clue outside the grid says how many towers you can see from that side; taller towers hide shorter ones behind them.

Tip: A clue of 1 puts the tallest tower right at that edge. A clue equal to the grid size forces the towers to rise 1, 2, 3 and onwards in order.

Futoshiki

Place 1 to N once in every row and column. Every inequality sign between two cells must hold, with the point facing the smaller digit.

Tip: A cell that is smaller than a neighbour can never hold the largest digit, and a chain a < b < c pushes a down and c up.

Suguru

Each outlined region holds the digits from 1 up to its size, once each. Two cells that touch, even diagonally, never hold the same digit.

Tip: A one-cell region is always 1, so none of its eight neighbours can be 1. Look for digits a region still needs that can only go in cells next to the same outside cell.

Straights

Fill the white cells so no digit repeats in a row or column, counting the digits on black cells. Each compartment of white cells between black cells holds a run of consecutive digits, in any order.

Tip: In a 9×9, a compartment of five cells always contains 5. Work out which runs still fit a compartment, then rule their certain digits out of the rest of the line.

Inshi no Heya

Place 1 to N once in every row and column. Each room is a run of cells within a row, and its number is the product of the digits inside.

Tip: Factorise first: in a 6×6, a two-cell room of 30 can only be 5 and 6. Rooms with a prime factor like 5 or 7 pin that digit into the room.

Ripple Effect

Each outlined region holds the digits from 1 up to its size, once each. Two equal digits in a row or column need at least that many cells between them.

Tip: A 1 blocks only its four direct neighbours, but a 4 reaches four cells in every direction. Place the big digits early: they rule out the most.

Renzoku

Place 1 to N once in every row and column. A dot between two cells means their digits are consecutive, and every such pair has a dot.

Tip: A cell with dots on both sides in a row needs one neighbour a step below it and one a step above, so it can’t be 1 or N. No dot is just as useful: it rules out both digits next to yours.

Sum Skyscrapers

Place towers of height 1 to N once in every row and column. A clue outside the grid is the total height of the towers visible from that side.

Tip: A clue equal to N means only the tallest tower is visible, so N stands right at that edge. Every clue includes N itself, so subtract N and ask which shorter towers make up the rest.

Questions

Is Hoot’s Puzzles free?

Yes. Every puzzle is free to play, with no adverts and no tracking. Your progress is kept in your own browser, and an optional account can sync it between devices.

How hard are the puzzles?

Each type has four ranks. Lemma is a warm-up, Proposition needs an idea or two, Theorem is near-minimal and Conjecture uses the fewest clues and the hardest techniques.

Can every puzzle be solved without guessing?

Yes. Every puzzle is checked to have exactly one solution that can be reached by logic alone, and Professor Hoot’s hints show the next logical step.

How do the puzzle numbers work?

There are 99,999 puzzles per type and rank. Each has its own number, so you can replay a puzzle or share it with a friend by its number.

Can I move my progress to another device?

Yes. Copy your progress code on one device and paste it on the other.

Guides

Rules, tips and worked examples from Professor Hoot. Start with the solving techniques guide or browse all guides.

Sudoku variants

Number puzzles

Your progress

Playing on another website or device? Copy your progress code here, then paste it into the other copy of the game. Your solved puzzles, best times, daily streak and current puzzle come with you.

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