Play Number Loop Online Free: Rules, History & Strategy

Imagine a grid sprinkled with numbers, and a single unbroken loop hiding inside it — a closed path that snakes between the dots, never crossing itself, never branching, obeying every clue along the way. Your job is to find that one true loop. Welcome to Number Loop, the deceptively simple line-drawing puzzle that loop fans around the world know as Slitherlink.

It is pure deduction with no arithmetic and no guesswork required. If you have ever enjoyed connect-the-dots as a child, Number Loop is the grown-up logician's version — and once it clicks, it is genuinely hard to put down. You can jump straight in at /play/number-loop, or read on to learn the rules, the history, and the tactics that turn a baffling grid into a satisfying solved loop.

The history of Number Loop

Number Loop is better known by its original name, Slitherlink — and it is a genuine original from Nikoli, the legendary Japanese publisher that also popularized Sudoku. It first appeared in Puzzle Communication Nikoli #26 in June 1989. According to puzzle historians, a Nikoli editor combined two separate reader-submitted ideas into the loop puzzle we know today; those earliest versions numbered every cell and did not yet enforce the single-loop rule, which was soon refined into the sparser, more elegant form players love now (source).

The puzzle travels under many names: Slitherlink, Fences, Loop the Loop, Loopy, Takegaki, Sli-Lin, and Suriza all describe the same idea (source). It spread worldwide through Nikoli's English-language puzzle books and through video-game adaptations on the WonderSwan, Game Boy, and Nintendo DS, eventually earning a place beside Sudoku as one of the most recognized logic puzzles on the planet (source).

How to play Number Loop

The rules fit in a single breath, but the depth runs deep. Here is everything a beginner needs.

1. Understand the goal. Draw one single, continuous loop along the edges between the dots. The loop must close on itself with no loose ends.
2. Obey the numbers. Each numbered cell tells you exactly how many of its four surrounding edges belong to the loop. A 3 means three of its four sides are part of the loop; a 2 means two; a 1 means one; a 0 means none.
3. Respect empty cells. Cells without a number can have any number of loop edges — they carry no constraint, so ignore them as clues.
4. Never branch or cross. The loop is a single ring. It cannot fork, cross over itself, or split into two separate loops.
5. Mark what you know. On /play/number-loop, click an edge to draw it as part of the loop, and mark edges you have ruled out with an X. Tracking the "no" edges is just as important as the "yes" edges.
6. Finish the loop. When every numbered clue is satisfied and a single unbroken loop runs through the grid, the puzzle is solved.

Strategy & tips

Number Loop rewards patient chains of small certainties. These tactics will get you from staring blankly to steadily filling the grid.

Start with the 0s. A 0 is the friendliest clue on the board: every one of its four edges is empty. Cross them all out immediately. Each X you place ripples outward, restricting neighboring cells.

Hunt for 3s, especially adjacent ones. World-class solver Thomas Snyder ("Dr. Sudoku"), a multiple-time World Sudoku Champion and editor at Grandmaster Puzzles, advises starting with the most constrained clues. As he explains, 0s force every surrounding edge empty, while adjacent or corner 3s force loop segments — and a pair of side-by-side 3s is a top opening pattern, because the shared edge between them must be drawn, as must the two outer edges (Snyder, GMPuzzles).

Track every dot, not just the numbers. Puzzle programmer Jonathan Olson, author of an in-depth Slitherlink methodology, points out that each dot touches exactly 0 or 2 loop segments — never 1 or 3. So the moment a dot has two segments, you can cross out its remaining edges; and a dot with one segment must sprout a second. Chaining these dot deductions, Olson notes, solves much of the grid without ever guessing (Olson's Slitherlink guide).

Watch the corners. A 3 in a corner forces both outer edges of that corner. A 1 in a corner forbids both outer edges. Corner clues are often the easiest place to anchor your first confident lines.

Avoid premature closure. Never close a small loop that leaves numbered clues outside it. There is only one loop, and it must satisfy every clue — so if connecting two ends would seal off the loop too early, that connection is wrong.

If you enjoy this kind of edge-by-edge reasoning, you will likely love the deduction in Star Battle and Nonograms, which reward the same patient elimination. Number-lovers can pivot to Sudoku or Kakuro for a different flavor of logic.

Is Number Loop the same as Slitherlink?

Yes — Number Loop is simply another name for Slitherlink, the Nikoli loop puzzle also called Fences, Loop the Loop, and Loopy. The rules are identical.

Do you need to be good at math to play Number Loop?

No — Number Loop requires no arithmetic at all; the numbers are constraints to count against, and the entire puzzle is solved with pure visual logic.

Watch a video tutorial

Seeing a loop come together step by step makes the rules click instantly. These reputable walkthroughs are a great place to start:

• Slitherlink Tutorial: How to solve a Slitherlink logic puzzle (HD) — YouTube tutorial
• How to Solve a Slitherlink Puzzle — YouTube
• Slitherlink Tutorial - #1 Rules — YouTube

Ready to draw your first loop?

The fastest way to learn Number Loop is to play it. Start with a small grid, cross out the edges around every 0, hunt down those adjacent 3s, and watch the loop reveal itself one certain line at a time. Want a fresh challenge every day? Check the daily puzzles for a new grid to conquer, then branch out to siblings like Ripple Effect when you want a change of pace.

Play Number Loop free now at /play/number-loop — no sign-up, no downloads, just one loop waiting to be found.