3-10 min
One Stroke Puzzle

One Stroke Puzzle

Puzzle

Trace every line in the figure exactly once without lifting the pen. Six levels, a fresh figure every time.

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Home / Puzzle / One Stroke Puzzle

One Stroke Puzzle is a free online one line drawing game. A figure of dots and dotted lines appears on a sheet of paper, and you have to trace every line exactly once without lifting the pen and without going over any line twice. It is the classic 一笔画 puzzle, and behind it sits a real piece of mathematics: a figure can be drawn in one stroke only when every dot has an even number of lines, or exactly two dots have an odd number — and those two are then the only places you are allowed to start. The game rings those dots for you, so the rule is something you learn by playing rather than something you have to be told. Every figure is generated by walking a pen across the grid without repeating a line, which means each one ships with its own solution rather than being scattered and hoped for. Six levels, from a seven-line square grid to a thirty-three-line lattice with diagonals. No timer, no download, no account.

How to play One Stroke Puzzle

  1. A figure of dots joined by dotted lines appears. Every dotted line has to be traced exactly once.
  2. Tap a dot to put the pen down, then tap a neighbouring dot to draw the line between them.
  3. You can also press and drag across the dots — the line follows your finger or your mouse.
  4. You may pass through the same dot as many times as you like. It is the lines that may not be repeated.
  5. You can never lift the pen: every new line has to start where the last one ended.
  6. If two dots have an odd number of lines, those two are ringed, and the stroke must start at one of them.
  7. If every dot has an even number of lines, the figure is a loop and you can start anywhere.
  8. Finish every line and the figure is solved. Undo takes back one line at a time; Clear starts the same figure again.

Tips

  • Count the lines at each dot before you start. Dots with an odd count are where a stroke has to begin or end, and there are only ever two of them or none at all.
  • When there are no odd dots the figure is a closed loop, so wherever you start you must finish in the same place. Pick a dot you are happy to come back to.
  • Leave the busiest dot until late. A dot with six lines needs three separate visits, and using them up early strands the rest of the figure.
  • Do not cut off a branch. If drawing a line would leave part of the figure with no way back to your pen, that part is lost — the game tells you the moment it happens.
  • On the diagonal levels, look for the long chains first. They have only one way through, so they effectively decide your route.
  • Undo is free of charge for the puzzle but not for the score. Three stars means no undos and no hints.
  • The Hint button never suggests a move that dead-ends — it checks that the rest of the figure is still finishable before offering one.
  • New Figure gives a genuinely different puzzle on the same level, so a level you have solved is worth replaying.

FAQ

Is One Stroke Puzzle free to play?

Yes. It runs in the browser with nothing to install, no account and nothing to buy. All six levels are included and unlock as you solve them.

Can I pass through the same dot twice?

Yes, as often as you like. The rule is about lines, not dots — every line exactly once, and the pen never lifts. A dot with four lines will be visited twice by any solution.

Why can I only start at certain dots?

Because of how the figure is built. Every time the pen passes through a dot it uses two lines — one in, one out. So a dot with an odd number of lines can only be where the pen starts or where it finishes. If a figure has two such dots, your stroke has to run between them, and the game rings both.

How do I know if a figure can be drawn at all?

Every figure here can. They are generated by walking a pen across the grid without repeating a line, so the walk that made the figure is itself a valid solution. A figure built by scattering lines at random usually has no solution and looks exactly the same on screen, which is why this game does not do that.

I got stuck with lines still left. Is that a bug?

No — it is the puzzle. Some routes cut off part of the figure and there is no way back, because the pen cannot jump. The game notices this the moment it happens and says so, rather than letting you keep clicking. Undo one line, or Clear and try a different route.

Is this the same as a connect-the-dots or pipe puzzle?

No. Connect-the-dots joins fixed pairs with separate paths and lines are optional. Here there is a single unbroken stroke and every line is compulsory, which is a completely different problem — it is the Seven Bridges of Königsberg, in puzzle form.

Are the figures always the same?

No. Each one is generated from the level number and the attempt number, so Replay reproduces the figure you were on and New Figure gives you a different one at the same size and difficulty.

Does it work on a phone?

Yes. The sheet is square and fills a portrait screen well, every dot has a hit area about three times its drawn size, and you can either tap dot to dot or drag your finger along the figure.