How to play Tectonic
Tectonic is also known as Suguru. Its board is divided into outlined regions of one to five cells, and you fill every cell with a number by following two rules. Every puzzle here has exactly one solution, and you can reach it by reasoning alone.
The rules
Each region holds the numbers from 1 up to its size, each exactly once. A region of three cells holds 1, 2 and 3, and a region of one cell holds 1.
Two equal numbers never touch: not side by side, and not at a corner.
How it differs from Sudoku
Tectonic has no rows, columns or boxes to complete. A row or a column can hold the same number more than once, as long as the copies don’t touch. Regions have different sizes and shapes, so each region has its own set of numbers, and no number is larger than 5.
Reading the board
Thick lines outline the regions. A small region limits its cells: a cell in a region of two cells can only hold 1 or 2.
A cell touches up to eight others, diagonals included. Equal numbers in diagonal neighbours break the rule, even when they are in different regions.
Two cells of one region can’t hold the same number even when they are far apart, because each region uses each of its numbers once.
A number that breaks a rule is underlined, and the cell’s description says which rule it breaks.
Playing here
Select a cell, then press a number key from 1 to 5 or use the number pad. A number larger than the region’s size can’t be placed there. The arrow keys move the selection, and Home and End jump to the ends of a row.
Turn on Notes to pencil in the numbers a cell might hold. With a keyboard, hold Shift and press a number to add or remove a note, or press N to switch Notes on or off.
Erase, Backspace or Delete clears your number. The starting numbers can’t be changed. Undo and Redo step through your moves.
Pause hides the board until you resume.
On the Play page, choose a size and a difficulty, then how you want to play. Standard shows a timer and Relaxed hides it. With answer checking on, each entry is compared with the solution. Your choices apply to new puzzles.
Hints
Hint opens a short ladder of help. It starts with where to look, then names the technique, then explains why it holds, and the last step makes the move. Hints reason from the numbers on the board, not from your notes, so a missing or wrong note never becomes part of an explanation. If one of your numbers breaks a rule or doesn’t match the solution, the hint tells you first, and says when it is comparing with the solution rather than reasoning. Press H for a hint and Esc to close it.
Difficulty and size
Size and difficulty are separate choices. A 6×6 board is a shorter puzzle and an 8×8 board has more regions, while the difficulty describes the reasoning a puzzle needs:
Easy needs only singles: Single-cell region, Last digit, Only digit left and Only place in the region.
Medium adds Shared neighbour.
Hard adds pairs and triples, within a region and among cells that touch.
Statistics count each size and difficulty on its own, so a time on one is never compared with another.
Saving your games
Your Tectonic games are saved in this browser as you play, and each puzzle you start is kept separately, so you can come back to any of them from Your games. If the browser isn’t keeping data, the page tells you. Sharing a puzzle shares its starting board, never your progress.
Lessons
Worked examples, each with a small diagram and its explanation:
Singles: the only number a cell can take, and the only place left for a number in its region.
Shared neighbour: a cell that touches every place a region’s missing number could go.
Pairs and triples: cells that share their last few numbers between them.