Light Grid

Press a cell and it flips — along with the four cells around it. The board starts scrambled; your job is to make it entirely dark, inside a move budget that is always achievable.

It runs entirely on your device: 0 network requests, works offline. No ads, no account, nothing to buy, and no betting, money or prizes of any kind.

1. Focus the board — click it, or press Tab until it is focused.
2. Move with the arrow keys. The cursor is outlined, not just tinted.
3. Press with Enter. That cell and its orthogonal neighbours all flip.
4. Watch the marks. Each cell shows odd or even — how many times you have pressed it. Pressing a cell twice undoes it entirely, so only the odd ones are still doing anything.
5. Clear the board before the moves run out.

How do you solve a lights-out style toggle puzzle?

Stop thinking about order and start thinking about parity. Pressing a cell twice cancels out, so the only thing that matters is which cells you press an odd number of times — the sequence is irrelevant. That means you can work top-down: once you have decided what to press in the top row, every row below is forced, because the only way to switch off a lit cell is to press the one directly beneath it. Choose the top row, let the rest follow, and check whether the bottom clears.

Is every board actually solvable?

Yes, by construction. Boards are made by starting from a fully dark grid and applying random presses, so undoing that exact set always works — an impossible board cannot be generated. The move budget is then computed by solving the board and adding a small margin, so it is always achievable and always tight enough to require planning.

Why does it tell me how many times I have pressed a cell?

Because that is the insight the puzzle is built on, and hiding it just makes the game harder to learn without making it more interesting. Once you can see which cells are at odd parity, you can reason about the board instead of experimenting on it.

Does it work offline?

Yes. Once the page has loaded once, the whole game is on your device — rules, board, everything. There is no server involved in play at any point.

Is there any money, betting or in-app purchase in this?

None, and there never will be. No currency, nothing to buy, no lives to refill, no wager of any kind.

Can I play it with a keyboard or a screen reader?

Both. Arrows move, Enter presses, and the board publishes a row-and-column description so a screen reader can announce which cells are on and where the cursor is. Lit and dark are shown by a glyph as well as by colour, so nothing depends on telling hues apart.

Five by five, seven scrambling presses, and a budget of the true minimum plus three. The minimum is computed by solving the board rather than estimated, so the difficulty rating is real.

Colour Code is the other deduction game here — it asks you to infer a hidden sequence from numeric feedback rather than to plan a route.

Bookmark this page (Ctrl+D, or ⌘D on Mac) or install the app — it works offline the next time you need it.