0h n0

0h n0 turns rows and columns into lines of sight. Numbered blue dots tell you how many other blue dots they can see, red dots close the view, and each blank must be settled by deduction. The browser edition offers free play and a daily-puzzle route with barely any ceremony.

What is 0h n0?

The board speaks in two colors and one wonderfully nosy rule. Blue dots look along their row and column, their numbers declare how many blue companions should be visible, and red dots act like tiny curtains. Filling every blank means deciding where sight must continue and where it must stop. The idea comes from Kuromasu, but creator Martin Kool gave this companion to 0h h1 its own spare, repeatable rhythm. Current menus expose free play, today's puzzles, hints, elapsed-time controls, themes, and an optional competitive sign-in layer, so the puzzle can stay a quiet solo exercise or acquire a stopwatch and scoreboard.

What you can do there

• Deduce which blank dots must be blue or red
• Solve free-play or daily visibility puzzles

Why we picked it

The rules fit on a few short lines, yet every clue reaches beyond its own cell and tangles with the rest of the grid. That makes even a small board feel pleasantly interconnected: one red blocker can settle several sight lines at once. The page also gets out of the way quickly, putting the puzzle before the furniture.

How to get the most from it

Read the How to play panel first, then begin with a 5-by-5 board. Mark a blank blue when a sight line must stay open and red when it must stop; contemporary versions cycle a cell from blank to blue to red. Work from clues that are already boxed in, and use the hint or undo control when the grid starts arguing back.

Good to know

Free play is available from the browser landing page. Sign-in is presented as an optional route to achievements, experience points, and leaderboards, not a gate in front of the puzzle. The site still advertises older phone editions, but current app availability, touch behavior, sound, accessibility, offline use, and cross-device parity have not been established.

Who made it, and when?

Martin Kool is the credited creator or organization. The earliest supported launch date we found is February 12, 2015.