Thread

How it works

What you get from it

Logic you can feel under your finger. You trace the route as you think it. Every square you settle narrows where the line can go next.

It trains looking a few squares ahead. A corner or a pocket of squares shows up before you reach it. Seeing it early saves a cut.

Easy is a quick one on a 6×6 with plenty of numbers. Hard is a 9×9 with walls and fewer numbers to lean on.

Rules

A square grid with numbers on some squares. Draw one line that starts on 1 and moves square to square, up, down, left or right, never diagonally. It passes through every square exactly once, meets the numbers in order and ends on the last one. Exactly one line fits.

On medium and hard, a few walls sit between squares. The line can’t cross them.

How to play in Rather

Put your finger on the line and drag to draw on. Drag back along it to take squares off. Starting in the middle of the line cuts it there first.

Taps work too. Tap a square next to the line’s end to draw on to it. A tap on the line cuts it back to that square. A tap on 1 clears it.

The line won’t step onto a number out of turn, cross a wall or visit a square twice. Reaching the last number early is fine: the board waits until every square is on the line.

One drag is one Undo step. On a keyboard, the arrows draw on from the end and Backspace steps back.

Where to start

Start in the corners. A corner square has only two neighbours, so unless it holds 1 or the last number, the line uses both.

Then work along the edges and beside walls. A square with only two ways left takes both. Once a square has its two pieces of line, every other way through it is closed.

Check both ends. When number 1 has only one free neighbour, the line leaves that way. The last number works the same from the other side.

Mind the order. Joining two stretches of line is out when it would skip a number, for example going from 3 straight to 5.

A loop is never right. Neither is a route that leaves a pocket of squares behind with no way for the line to get in and out again.

When you’re stuck

Tap Hint. If your line has left the way through, it cuts it back to where it went wrong: “This one doesn’t fit.” Otherwise it draws on through every square the rules settle, up to the next number. It says why: “Going here would skip number 4.”

The new squares glow once. There is no Errors in Thread: the board keeps the walls, the order and “no square twice” for you.

Undo takes back a whole drag at a time.

Sizes

• Easy 6×6 8 to 12 numbers, no walls.
• Medium 7×7 6 to 9 numbers, up to 4 walls.
• Hard 9×9 4 to 12 numbers, up to 8 walls.

Questions

Can the line go diagonally?

No. Only up, down, left or right, one square at a time.

What if I reach the last number too early?

Nothing breaks. The puzzle is solved only when every square is on the line, so cut back and try another way.

Is there only one way to draw it?

Yes. Every puzzle has exactly one line that fits. The hint follows it.