Drawing on a touchscreen, and on a keyboard
This is the one genre here where the input really matters, because you are tracing a route rather than tapping cells. Drag your finger and the line follows; drag back over yourself and it retracts, which is far quicker than undoing step by step when you have gone wrong.
On a desktop the arrow keys extend the line one cell at a time and backspace retracts it, which is the precise way to work when a board comes down to a couple of contested cells. Both methods are equal; long boards tend to start as a drag and finish on the keyboard.
Nothing to install, nothing to join
It runs in the browser. Your progress, times and streak sit on this device and go nowhere, which is why there is no account to make. Clearing site data clears them, and there is an export in settings for moving between devices.
After one visit it works offline, today’s boards included. Add it to your home screen if you want it to open full screen like an app.
What you are looking at
The numbered cells are waypoints. Your line has to pass through 1, then 2, then 3, in that order, and it must also pass through every other cell on the board exactly once, without crossing itself.
A partly drawn line is saved as you go, so you can close the tab mid-board and pick it up later. Undo steps back one cell at a time and there is no limit on it.
If it will not come out
Almost always the problem is a cell you have stranded - somewhere the line can no longer reach without breaking a rule. Check the corners and edges first; they run out of options long before the middle does.
The hint button will point at the next forced step and tell you why it is forced, rather than just filling it in. On the Daily it costs nothing and never will.
Common questions
How do I draw the line?
Drag a finger or the mouse and the line follows. Dragging back over yourself retracts it, which is much quicker than undoing step by step. On a keyboard the arrow keys extend and backspace retracts.
Is there an app?
No separate app and nothing in a store. It runs in the browser and can be added to your home screen, where it opens full screen with the same puzzles.
Does it cost anything?
No. The daily board, the archive and the endless mode are all free, and there is no account to buy anything with.