Fern Mire Coils

Fern Mire Coils is a quiet grid puzzle about a single winding body of cells that runs from a marked head to a marked tail and never once brushes against itself.

HOW A BOARD WORKS
Every board is a square grid with a ringed head marker and a pointed tail marker. Numbers along the top and down the left edge say exactly how many cells of the coil belong in each column and in each row. Your job is to find the one route that satisfies every count.

The coil is one cell thick. Each of its cells touches exactly two others along an edge, apart from the head and the tail, which touch only one. And then the rule that makes this puzzle its own thing: the coil may never brush itself corner to corner. The only diagonal contact allowed is the one a bend makes as it turns. In practice that means no solid two by two square of coil anywhere, and no two stretches of the body sliding past each other on a diagonal.

DRAWING THE COIL
Tap a cell to move it from open water, to coil, to ruled out, and back again. Drag across a run of cells to lay a whole stretch at once, with a brush switch under the board deciding whether a drag paints coil or rules cells out. The counts talk back as you work: a number turns green the moment its row or column is exactly right, and red the moment you overshoot, so a wrong turn shows itself early.

Undo steps back through your marks one stroke at a time. Check outlines every cell that breaks a rule right now, whether that is a piece of body with three neighbours, a solid block, or two stretches brushing corners. Nudge settles one more cell when a board has you properly stuck, and boards finished without a nudge feed your unaided run.

THREE SIZES, THREE BODY LENGTHS
Play on 8 x 8, 10 x 10 or 12 x 12, and choose whether the body should be slim, standard or full. Every board is built fresh on your phone and put through a solver before you ever see it, so each one has exactly one answer and can always be reasoned out from the numbers. Nothing here needs a guess.

WHAT YOU WILL NOT FIND
No internet connection is used or required, ever. The whole app works in flight mode. There are no adverts, no trackers, no accounts, no sign-in, no purchases and no sound of any kind. Feedback is entirely visual, with an optional haptic tick you can switch off. Your finished boards, best times and badges live on your device and nowhere else.

A LOGBOOK AND TWELVE BADGES
The stats screen keeps your finished boards, your best time for each size, total time spent tracing, coil cells painted and your current unaided run. Twelve naturalist badges mark the milestones, from your first finished coil to a thousand cells painted across every board you have ever traced.

Marshland colours, a soft serif and a board drawn entirely in code: no images to download, no updates to chase. Just a fen, a coil, and the numbers along the edge.