Slitherlink FAQ

Slitherlink is a logic puzzle played on a grid of dots. Some cells contain a number from 0 to 3, which says how many of that cell’s four sides are part of the answer. You join neighbouring dots with horizontal and vertical lines to make one single closed loop that never crosses or branches, so that every number is correct. It is also known as Fences, Loop the Loop, and Takegaki, and is often just called a loop puzzle.

Yes. slitherlink.app is completely free and runs entirely in your browser. There is nothing to buy, download, or install, and there are no interruptive video ads, premium tiers, or paywalls. Open the page and a puzzle is already waiting.

No. The game is the website — a 100% browser-based build with no app store download and no sign-up. Your best times and streaks are saved locally in your browser, so there is no login to manage.

Slitherlink is a loop puzzle popularised by the Japanese puzzle publisher Nikoli, which published it as “Slitherlink” (スリザーリンク) from the late 1980s and made it a staple of its magazines. Related puzzles appeared earlier under other names, and the same idea is known in English as Fences, Loop the Loop, and Dotty Dilemma.

It is the same puzzle with the same rules — join the dots into one loop so each number is correct. This build adds instant new puzzles in three grid sizes, drag drawing, an X tool, unlimited undo and redo, a mistake check, synthesized sound with a mute, and a layout that fits a phone screen. It is an independent site and is not affiliated with those sites.

Draw lines between neighbouring dots. Each number must have exactly that many lines around its cell, every dot must have either zero or two lines touching it, and all the lines together must form one closed loop with no crossings, branches, or separate loops. Use X marks to record gaps that cannot hold a line. When the loop closes and every clue is satisfied, the puzzle is solved.

A number in a cell is the count of that cell’s four sides that are drawn as lines. A 0 means no sides are used, a 1 means exactly one side, a 2 means two, and a 3 means three. Cells without a number can have any number of lines around them. Once a number is fully satisfied it dims on the board, and if you draw too many it turns red.

Tap, click, or drag between dots to draw lines. Right-click, or switch to the X tool, to mark a gap as “no line”. On the keyboard, U undoes, R redoes, C checks for mistakes, X switches tool, N starts a new puzzle, and M toggles sound. Ctrl+Z and Ctrl+Y also undo and redo.

Check compares your board with the puzzle’s unique solution and flashes any drawn line that does not belong to it, plus any X you placed on a gap that is actually a line. It does not fill anything in for you and the highlight fades after a few seconds or on your next move. Use it sparingly if you want a pure solve.

An X marks a gap that you know cannot hold a line. It has no effect on whether the puzzle is solved — only lines count — but X marks are how you keep track of your deductions, and dragging with the X tool marks a whole run of gaps at once.

Yes. Each puzzle is generated from a random closed loop, and clues are then removed one at a time. A removal is kept only when a solver confirms the puzzle still has one and only one solution. That means the answer never depends on a coin-flip, although larger 10×10 puzzles can need you to follow a path several steps ahead.

Begin with the certain moves: X all four sides of every 0, draw the three sides around a 3 that touches a 0, and use both outer sides of a 3 in a corner. Then work dot by dot: a dot with two lines gets X marks on its remaining gaps, and a dot with one line and a single open gap must continue through it. See the tips page for the full pattern list.

5×5 is a warm-up that usually takes a minute or two, 7×7 is the standard size and takes several minutes, and 10×10 is the challenge with long loops and sparse clues. Each size keeps its own best time and streak, so switching sizes never damages a record.

Look at every dot that already has a line and count its open gaps; look at every number that already has its full count and X the rest. If nothing is forced, think about inside and outside: the loop divides the board into two regions, and two cells that are neighbours are on the same side unless a line separates them. Undo is unlimited, so you can also test a line and take it back.

The current streak counts consecutive solved puzzles at one grid size. Starting a new puzzle or clearing the board after you have drawn something, without having solved it, counts as giving up and resets that size’s current streak to zero. Your longest streak is kept separately.

Your best time, solve rate, streaks, chosen grid size, and sound setting are saved locally in your browser. Nothing is sent to a server and there is no account. Because the save lives on the device, a different phone, a new browser profile, or cleared site data looks like a fresh start. A puzzle in progress is not saved if you close the tab.

Yes. The layout is built for touch: tap a gap between two dots to draw a line, drag to draw several at once, and use the Line / X button under the board to switch to X marks. The board and all controls fit on one portrait screen, and starting a new puzzle is instant with no page reload.

The game needs a connection to load the page the first time. After that, the puzzle generator runs entirely in your browser, and some browsers may keep the tab playable without a network, but there is no dedicated offline app or installer.

Open Stats from the chart icon above the board and use Reset progress, then confirm with the second tap. That clears best times, solve rates, and streaks for all three grid sizes on this browser. It cannot be undone.

Any current browser with JavaScript: Chrome, Edge, Firefox, and Safari on desktop, plus their mobile versions. If the board does not respond, update the browser, allow scripts for this site, and reload.