Guide
How to Play Slitherlink
Slitherlink is a game of deduction. Read the numbers, rule out impossible edges, and draw one closed loop through the dots that makes every clue correct.
Play SlitherlinkThe objective
Draw one loop that satisfies every number
Slitherlink is played on a rectangular grid of dots. Some cells hold a number from 0 to 3. You win when you have drawn lines between neighbouring dots that form a single closed loop — no crossings, no branches, no loose ends — and every number matches the count of that cell’s sides used by the loop.
Nothing in the puzzle is random once it is generated: every grid has exactly one answer that can be reached by reasoning. The clock runs from your first line, but there is no move limit and undo is free, so the only challenge is deduction.
The game is free, runs in the browser, and needs no account. Open the board when you want to play; use this guide for the rules, the grid sizes, and the habits that solve puzzles faster.
The grid
Dots, gaps, and a handful of numbers
A 7×7 puzzle has 49 cells, 64 dots, and 112 gaps between neighbouring dots. Each gap is either a line in the final loop or empty. Numbers sit inside cells: a 0 means none of its four sides are lines, a 3 means three of them are. Blank cells can have any count.
Every puzzle is generated fresh in your browser. A random loop is drawn first, its numbers are written down, and then numbers are removed for as long as the puzzle still has only one solution.
Controls
Tap, drag, or use the keyboard
Every method edits the same board. Pick whichever fits the device in your hand.
Everywhere
Tap, click, or drag
Tap or click a gap between two dots to toggle a line. Press and drag to draw or erase a run of edges in one stroke — one stroke is one undo step. The closest gap to your pointer is always the one that changes.
Touch & mouse
X tool / right-click
On a phone, tap the Line / X button under the board to switch tools. On a desktop, right-click a gap to place or remove an X mark without changing tools. Dragging with the X tool marks a run of gaps.
Desktop
Keyboard
U undoes, R redoes (Ctrl+Z and Ctrl+Y work too), C checks for mistakes, X switches between Line and X tools, N starts a new puzzle, and M mutes the sound. Every on-screen button has a visible focus ring.
The loop
Four steps you repeat all puzzle
Read a number, draw or mark an edge, check the dots it touches, and repeat until the loop closes.
- 1
Read the grid
The board is a grid of dots with numbers from 0 to 3 in some of the cells. A number tells you how many of that cell’s four sides are part of the final loop. Cells with no number are unconstrained.
- 2
Draw lines between dots
Tap or click the gap between two neighbouring dots to draw a line, or drag across several gaps to draw a whole run in one stroke. Lines are only horizontal or vertical and always join two adjacent dots.
- 3
Mark what cannot be a line
Switch to the X tool (or right-click) to mark a gap as “no line here”. X marks are your notes: they stop you from drawing a line you already ruled out and make the next deduction easier to see.
- 4
Close one single loop
Every dot ends up with either zero or exactly two lines. The lines must join into one closed loop that never crosses itself or branches. When every number is satisfied and the loop is closed, the puzzle is solved.
Rules & timing
Every rule that decides an edge
The objective
Connect neighbouring dots with horizontal and vertical lines to make one closed loop. Every numbered cell must have exactly that many of its four sides in the loop.
One loop, no branches
The loop never crosses itself, never branches, and never has loose ends. So every dot the loop touches has exactly two lines, and every other dot has none. Two separate loops is not a solution.
What the numbers mean
A 0 means none of the cell’s sides are used, a 1 means one side, a 2 means two, and a 3 means three. A 4 cannot appear because four sides would close a tiny loop by itself. Blank cells can have any count from 0 to 4 lines around them.
Unique solutions
Every puzzle here has exactly one solution. The generator draws a random loop, writes the clues from it, then removes clues one at a time and keeps a removal only if a solver confirms the puzzle still has a single answer.
Timing and streaks
A clock starts on your first line and stops when the loop closes. There are no scores or hints to spend. Best time, solve rate, and streak are tracked per grid size, and starting a new puzzle before finishing resets that size’s current streak.
Grid sizes
Three sizes, one rule set
The only setting in Slitherlink is the size of the grid. Pick it above the board; best times and streaks are kept separately for each.
- 01 · Warm-up — a minute or two
5×5
Twenty-five cells and around ten clues. Ideal for learning the rules, practising the basic patterns, or a quick break. Most 5×5 puzzles fall to the simple 0, 3, and dot rules alone.
- 02 · Standard — several minutes
7×7
Forty-nine cells and around twenty clues. The default size: large enough that you need to track how partial paths join up, small enough to finish in one short sitting.
- 03 · Challenge — a proper sit-down
10×10
One hundred cells and around 35 clues. Long loops, sparse numbers, and regions that only resolve once you have chased a path around the board. Expect to lean on X marks and on inside / outside reasoning.
Common mistakes
Why solvable puzzles get stuck
Drawing on a guess
A line you are only “pretty sure” about can quietly poison ten later deductions. Prefer a certain X over a hopeful line, and use the mistake check early rather than late.
Forgetting the dead ends
A path end with only one open gap left is not a choice — it must continue. Scan the ends of your drawn paths regularly; that is where most stuck boards hide their next move.
Closing a small loop
Two path ends meeting is only correct if that closed loop covers every line on the board. If unmet numbers remain, the join is an X, however natural it looks.
Ignoring the numbers around a satisfied cell
Once a number has its full count of lines, its remaining sides are all X. The number dims on the board when it is satisfied — use that as a cue to mark the rest.
- Start with the 0s: put an X on all four sides. Then look at every 0’s neighbours — the shared side is already ruled out.
- A 3 next to a 0 needs its other three sides. A 3 in a grid corner always uses both of its outer sides.
- Two 3s side by side: draw the line between them, plus the outer side of each 3 on the far end. Together those three parallel lines are always part of the solution.
- Corner 1s are easy: both outer sides of a 1 in a grid corner are ruled out, so put X marks on them.
- Look at every dot: it ends with zero or two lines. If a dot already has two lines, X the rest. If it has one line and only one open gap left, that gap must be a line.
- Do not close a loop early. If two path ends could join into a small loop while other clues are still unmet, that join must be an X.
- Mark X liberally. Every X you place makes a neighbouring dot or number easier to finish, and undo is free if you were wrong.
- When stuck, think inside and outside: the loop splits the board into inside and outside cells, and two neighbouring cells are on the same side unless a line runs between them.
Where you can play
Same game on phone and desktop
slitherlink.app runs in any modern browser with no app to install. Progress stays on the device you played on.
Desktop browsers
Chrome, Edge, Firefox, and Safari all run the game with no plugin. Click and drag to draw, right-click for X marks, and use the keyboard shortcuts for undo, redo, check, tool, new puzzle, and mute.
Phones and tablets
The layout is touch-first. The board and the Line / X, Undo, Redo, Check, Clear, and New buttons all fit on one portrait screen, and dragging draws several edges at once.
Progress on this device
Best time, solve rate, and streaks for 5×5, 7×7, and 10×10 live in local browser storage, along with your sound setting. They stay until you reset them or clear site data, and they do not sync between devices.
Still stuck on a rule? Read the Slitherlink FAQ or jump in and play.
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