A Masyu loop fails when the line breaks one of three rules: a black pearl must be turned on with both arms straight, a white pearl must be passed straight through with at least one neighboring turn, and the path cannot cross or revisit any body cell except the starting pearl. The closing step is where most mistakes surface, because the browser only checks the local pearl shapes when you try to return to the start, not at the moment the line passes each clue. This guide explains which mistake to expect at each step, then walks through the keyboard sequence that closes a clean twelve-step route scoring 880 points on the Masyu Puzzle tool.
The Pearl Rules That Cause Most Masyu Mistakes
The single biggest source of mistakes is treating black and white pearls as interchangeable clues. They look similar on a board, but they demand opposite local shapes. According to Nikoli's published Masyu rules, a black pearl forces the loop to turn while it sits on the pearl and to keep going straight through both cells immediately next to it. A white pearl forces the loop to pass straight through the pearl itself and to make a ninety-degree turn in at least one of the two cells adjacent to it. Read those sentences back and you can already see why most broken attempts happen: solvers often put a turn on the white pearl (wrong, that must be straight) or pass straight through a black pearl (wrong, that must turn).
| Constraint | Black pearl | White pearl |
|---|---|---|
| Behavior on the pearl | Turn (ninety-degree corner) | Pass straight through |
| Immediately adjacent cells | Both arms must continue straight | At least one neighbor must hold a turn |
| Direction of escape | Forced away from the turn's outside | Free to continue straight or bend next door |
| Most common mistake | Forgetting one of the two straight arms | Forgetting to turn in the neighboring cells |
On the four by four Masyu board the upper-left pearl is black and the cell immediately to its right is white. That single arrangement already pins down the start of the solution: the loop must turn at the black pearl, so the first extension cannot be straight down, it has to be straight right, which then runs into the white pearl and forces a turn in one of the next cells. Anyone who begins by going down from the start violates the black-pearl rule on the very first accepted step and will not see the warning until they try to close the route many moves later.
Loop Structure Mistakes That Block the Close
The pearl rules tell you what each clue forces locally. The loop structure rules tell you what the whole path has to look like, and there are three structural constraints that the browser checks when you try to close the route. Each one produces a different kind of mistake, and each one is invisible until the closing keypress.
- Reusing a body cell. Every arrow move must land on a cell that is not yet part of the route. Stepping into a cell already in the path is treated as a detected dead end because a simple loop cannot reuse a body cell. If your cursor feels stuck with no useful arrows, that is almost always because the only valid neighbors are already painted.
- Closing too early. Returning to the starting cell closes the route, but the close only counts if every pearl sits on the path, every body cell is unique, and the local shapes around the pearls are correct. A premature close that misses even one pearl is reported as invalid and cannot be extended further, so the only fix is to press Restart and try again.
- Going off the grid. Leaving the four by four perimeter does nothing because the keypress is ignored, but it is still a mistake because it costs you time and sometimes causes solvers to lose track of where the cursor actually sits. The active cursor has a visible outline, so use that outline to confirm you are still on the board before every arrow press.
Loop structure mistakes usually show themselves only when you press the closing key. By that point you have already committed to a route, so the practical fix is to keep the cursor outline in view, count your accepted steps as you go, and treat any step count above twelve as a warning sign that you have doubled back through an empty cell rather than the start.
Movement and Keyboard Mistakes on the 4×4 Board
The keyboard layer is small but it has its own failure modes. The path is stored as ordered four by four cell indices, and each extension is only accepted when the new index sits at Manhattan distance one from the current one and has not been used before (the starting index is the only one allowed to be revisited, and only to close). Pressing the wrong arrow direction is the most common input mistake: it lands on a cell, the cursor outline moves, and you are suddenly one step into a region that does not fit the pearl rule you just violated.
Two more input mistakes deserve attention. First, pressing Space or Enter on a non-start cell does nothing, so a player who expects any cell to begin the loop will see nothing happen and assume the board is broken. Second, the boss screen is reached by pressing Escape twice within 400 milliseconds, and the same double press returns to the puzzle. Many solvers press Escape once to pause, reveal the spreadsheet background, and then forget how to come back, which is a separate but very common stumble. If the boss screen seems to be missing, you almost certainly pressed Escape once, paused longer than 400 milliseconds, and then pressed it again — that sequence counts as two single presses, not one double press, and the puzzle just stays where it was.
How to Avoid Common Mistakes in Masyu Puzzle
Use this keyboard sequence to lay down the clean twelve-step route that the validator accepts and the score locks at 880.
- Move the cursor outline to the upper-left cell, then press Space or Enter to begin the route on the black pearl there.
- Press the right arrow key. The line extends one cell to the right and onto the white pearl, satisfying the black-pearl turn and beginning the white-pearl straight passage.
- Press the right arrow key again to keep the path straight through the white pearl and into the cell beyond it.
- Press the down arrow key to take the required neighbor turn of the white pearl and start running down the right edge of the board.
- Press the right arrow key to reach the right edge of the board, then the down arrow key repeatedly until the path reaches the bottom-right corner cell.
- Press the left arrow key to run the path straight across the bottom edge of the board toward the lower-left corner.
- Press the up arrow key to bring the path up the left edge of the board back toward the starting row.
- Press the up arrow key to close the loop on the starting black pearl. The browser checks that every pearl is on the route, that body cells are unique, and that the local shapes at the black and white pearls are correct.
- Read the score: twelve accepted steps on a starting value of 1,000 produces 1,000 minus 10 times 12, which equals 880. The status changes to solved and the score is locked in.
- Press the Restart control to wipe the path, restore the original cursor, and reset the score if you want to attempt a shorter or alternate route.
That sequence is the published compact perimeter solution for this fixture. If a step is rejected, the most likely reason is that you pressed an arrow key while the cursor was on a cell whose target neighbor was already in the route — that is the dead-loop symptom, and the fix is to press Restart rather than try to back out manually.
What the Validator Catches and What It Doesn't
The browser validates every accepted movement, but it only reports problems at the points where they actually matter. Leaving the grid is silently ignored. Stepping into a body cell already in the route creates a detected dead end at the moment of the move. Returning to the start closes the route; if the pearl rules or route structure are wrong, the closed route is reported as invalid and cannot be extended. That means a solver who breaks a pearl rule on step three will not see a warning at step three — they will only see a problem when they close on step thirteen or later.
For related local-rule reasoning across other loop-style puzzles, see the explanation of whether a Masyu loop can cross or reuse a cell. The same "no cell reuse, no branch" structure appears in Pipes, Numberlink, and the one-line puzzles, so the habit of tracking which cells are already painted will transfer directly.
Score, Restart, and Boss Screen Controls
The score formula is straightforward: the route starts at 1,000 and loses ten points for every accepted step, so the clean twelve-step route ends on 880. A route that takes more accepted steps than necessary still scores less, which is why the boss screen's spreadsheet background is best treated as a private escape rather than a scoreboard. The Restart control restores the original cursor, an empty path, the full 1,000 starting score, and the unsolved status. A best score may be stored in this browser's localStorage, but it is never uploaded or attached to an account, so wiping site data clears it.
Outside of the keyboard layer, the board is a transparent CSS grid rather than a canvas, every cell announces its row, column, pearl type, selection, and path membership, and there is no downloaded art, audio, timer, random service, or pointer-only gesture to worry about. That gives you a deterministic environment where the only things that can go wrong are the rules themselves and the order of your arrow presses.
Related Logic Puzzles for the Same Break
Masyu is a short logic break, not a measure of cognitive ability, and it pairs naturally with a few neighbors that share its "no branch, no reuse, one loop" backbone. Shingoki extends the pearl concept with numbered black and white circles that demand both shape and segment-sum clues. Heyawake, Hitori, and Pipes all reward the same careful inventory of what each cell is allowed to do. If you want a similar "avoid the classic mistake" walkthrough on a different fixture, the magic-square mistakes guide covers the same habit of checking each rule locally before closing the structure, and the same discipline carries over to hashis, shingoki, and the bridge puzzles.