🧩 Tectonic

How to Play

Tectonic is the puzzle nicknamed "no equal neighbours," and the nickname carries most of the rules. The board is split into blocks — irregular regions of connected cells, each with its own size. Fill every cell so each block contains the digits from 1 up to the block's size, each exactly once: a two-cell block holds 1 and 2, a five-cell block holds 1 through 5.

The rule that names the puzzle: cells touching horizontally or vertically may never hold the same number, and this applies everywhere — inside a block and across block borders alike. Diagonal neighbours are allowed to match, the detail that trips up newcomers. A 1 at a corner may sit diagonally beside another 1, but a 1 directly above, below, left, or right of it is illegal.

Every puzzle here has exactly one solution, so guessing is never needed. Enter numbers from the on-screen number pad or your keyboard, press P (or the pencil button) for candidate notes, and use Backspace to erase. Three mistakes end the puzzle; the hint button reveals a correct value when you are stuck, and a timer runs from your first move to the completed grid.

Example

Picture the top-left corner as a two-cell block, one cell directly below the other. It must contain 1 and 2 in one of the two orders. Now the upper cell is also horizontally adjacent to a cell in a neighbouring three-cell block. If that neighbour already holds a 2, the upper cell cannot be a 2 — adjacent cells may not match — so the upper cell must be 1, and the lower cell takes the 2.

One glance at a neighbour settled a whole block. The same logic scales: when a region is down to two empty cells and a neighbour blocks one of the missing digits, the order is forced.

Strategy & Tips

• Start with the smallest blocks; a two-cell block has only two orderings, and the neighbours usually break the tie.
• Keep the diagonal rule close: a matching diagonal is legal, so never drop a candidate just because a diagonal neighbour shares it.
• Use pencil notes heavily in large blocks, where holding five or six candidates in your head invites errors.
• Check each placement against its four orthogonal neighbours — the cell beside it or below it often kills a promising number.
• When a large block is nearly full the missing values are forced; scan its empty cells for any that cannot accept one.
• Long thin regions are the bottlenecks, since every cell in a strip has neighbours on two sides shrinking its options.

Variations & Difficulty Levels

Difficulty here is mostly block geometry. Easy boards use small blocks of two to four cells, quick to fill and easy to track. Medium boards mix block sizes, dropping a couple of large regions among small ones. Hard boards lean on large blocks of eight cells and up, where the challenge is remembering each region's needs and how its edges interact with everything around them.

Because the blocks are irregular shapes, no two boards look alike even at the same difficulty — the same cell count can be sliced into completely different layouts. If you enjoy this style of placement logic, you will find a different flavour of it in the rest of the games on the site.

Common Mistakes & Edge Cases

• Forgetting the neighbourhood rule crosses block borders — two cells in different blocks still cannot match if orthogonally adjacent.
• Assuming diagonals must differ, then deleting the one legal option a cell actually had.
• Miscounting a block's size and aiming for the wrong digits, quietly corrupting the whole region.
• Filling a large block greedily from its middle, then finding a needed digit walled off at the edge.
• A one-cell block is a genuine edge case: it holds only the number 1 and acts purely as an obstacle constraining its neighbours.

Frequently Asked Questions

Why is Tectonic called "no equal neighbours"?

Because of its central rule: orthogonally adjacent cells may never hold the same number — the constraint that gives the puzzle its shape and its name.

Do diagonal neighbours count as neighbours?

No — only cells touching horizontally or vertically are bound by the rule, so diagonals may freely hold the same number.

Can a block contain just one cell?

Yes. A one-cell block holds the number 1, and its main job is to restrict the cells around it through the neighbourhood rule.

What is the biggest block on any board?

Hard boards reach blocks of eight cells and up; the larger the region, the more digits you must track in your notes.

What happens after three mistakes?

The puzzle ends for that run. You can start a new board, and the timer from the failed attempt does not follow you.

Why does a block sometimes seem impossible to finish?

Usually an outside neighbourhood constraint is being overlooked. Re-read the cells touching the block's edges, or let the hint button show you the overlooked cell.