Daily logic puzzle
Slitherlink online, a new river every midnight.
Slitherlink is a loop puzzle: you draw one closed loop along the lines of a grid so that every number says how many of its four sides the loop runs along. Ours is called Otters, it is free, there is no account and no advertising, and a new one appears at midnight.
- a new loop at midnight, easy on Monday and nine by nine on Sunday
- exactly one solution, reachable by reasoning, checked by program
- hints that explain the technique, a two step Check, no red ink while you play
Today's river. The loop runs on the lines, not through the cells.
The rules
Three rules, and that is the whole game.
Slitherlink is also sold as Fences, Loop the Loop and Takegaki. The rules are the same under every name.
- Draw one closed loop along the grid lines. The otters need a single river: no branches, no crossings, no second loop.
- A number in a patch counts its sides. It says how many of that patch's four sides the loop runs along, from 0 to 3. A patch with no number says nothing at all.
- Exactly one loop fits every number. A cross on a side is your own note that the side stays dry.
Our name for it
We call it Otters.
The puzzle is known as Slitherlink. We call ours Otters because the loop is a river the otters swim, and a river has to come back to itself: one channel, no forks, no second river somewhere across the marsh. That is the single closed loop rule told as a picture.
The rules are untouched. If you have solved Slitherlink elsewhere, the corner rules, the 3 next to 3 pattern and the parity arguments all work here exactly as you know them.
Where to start
Three ways in.
The archive of past rivers is free as well and goes back a year: Otters archive.
- Play today's river
The daily puzzle, easy on Monday and nine by nine on Sunday, new at midnight.
- How to play Slitherlink
The rules with a worked example, the controls and the corner patterns worth learning.
- Practice sets
Sets by difficulty when one river a day is not enough.
One solution
A program says so, not a person.
Every puzzle we publish has exactly one solution, and it is a program that decides. The generator throws a candidate away unless the solver returns exactly one solution and unless a second solver, restricted to human style reasoning, finishes it without guessing.
You can see the check yourself: the file tests.mjs in the game folder runs it over thirty days in every size. In a loop puzzle that guarantee is worth a lot, because a wrong segment can look right until the loop fails to close at the far corner.
While you play, nothing goes red. A mistake is shown only by Check, in two steps: first how many segments are wrong and roughly where, then which ones. Hint works the same way, first the technique and the place, then the move.
Questions
Questions about Slitherlink.
What is Slitherlink?
A loop puzzle on a grid of dots. You join dots with straight segments to form one closed loop, and every number tells you how many of the four sides of its cell the loop uses. Cells without a number tell you nothing. It is also published as Fences, Loop the Loop and Takegaki.
Is it free here?
Yes. The daily puzzle, the practice sets, the archive going back a year, the hints and the Check are all free, with no account and no advertising. We sell printable puzzle books on the same site, and that is the whole business model.
Can there be two separate loops?
No. There is exactly one loop and it must be closed, with no branches and no crossings. A closed second loop somewhere else in the grid is the most common way a nearly finished solution turns out to be wrong, which is why Check counts segments rather than just saying no.
What does a zero mean?
That the loop does not run along any side of that cell. Zeros are the best place to start: they let you cross out four sides at once, and the crosses then force the neighbouring numbers.
Do I ever have to guess?
No, and that is checked rather than promised. Every published puzzle was solved by a program restricted to reasoning before it was allowed out. If you are stuck, Hint names the technique and the corner before it draws anything.
Where can I get more of these on paper?
In the Otters book: one hundred Slitherlink puzzles as a printable PDF in A4 and US Letter, with the solutions at the back. There is a free five puzzle sample to look at first. See the <a href="/puzzle-books/slitherlink-puzzle-book/">Slitherlink puzzle book</a>.
Related
More of the same.
One hundred of these on paper, with the solutions at the back: Slitherlink puzzle book (PDF, free sample).
All ten daily games are on one page: daily logic games.
Auf Deutsch: Slitherlink online spielen.