Loop Trace for beginners: count the sides and close one loop.
Learn the difference between dots, cell clues, lines and crosses. Load one checked three-by-three board, practise the edge controls, then follow an eight-line loop and verify every number.
Loop Trace is a numbered-cell loop puzzle. A number belongs to the square space between four dots. It tells you how many of that cell’s four sides carry lines. The dots themselves have no number and do not need to be visited. Your completed drawing must be one closed loop without a branch or crossing.
This is different from connecting numbered islands: the clues count the sides of cells, and the answer cannot branch. It is also different from filling squares to match run clues. Here your decisions belong on edges between neighbouring dots. Our implementation and examples use the familiar single-loop mechanic described in source [1], with our own clue sets, code and explanations.
Read a clue as a count of bordering sides
A 0 has no line on any of its four sides. A 1 has exactly one, a 2 exactly two, and a 3 exactly three. A side shared by two cells contributes to both counts. A number is not a direction and does not say how many cells to enclose. Some clues may sit outside the finished loop.
You can join only adjacent dots along a horizontal or vertical grid edge. Lines cannot run diagonally, skip a dot or end in the middle of a cell. At every dot used by the finished loop, exactly two line segments meet. One segment would leave an open end; three or four would branch or cross. Unused dots may have zero segments. Finally, all drawn segments must belong to the same loop. Two separate closed loops fail even if their nearby numbers match.
Practise the three edge marks
Choose an edge to cycle unmarked → line → cross → unmarked. A cross is a note that you intend to leave an edge unused. It does not count as a line and is not a barrier with special rules. Unused edges may remain unmarked when you win; you do not have to cross out the whole board.
For a keyboard, Tab reaches edge buttons and Enter or Space changes the focused edge. Right and Left move forward or backward through the labelled edge list; they do not draw a line. Each edge label states its identifier, orientation, row and column, and whether it is unmarked, a line or a cross. The expandable ledger also lists the clues’ current counts, so you need not rely on colour.
Each change to an edge adds one edit, even if it removes a line. Undo last edit restores the previous marks and reduces Edits by one. The controls allow wrong lines while you work: adding a line that overfills a clue or creates a branch is not a correct-move hint. Check loop reports your current counts, open ends, branching dots and line groups; it does not choose the next edge.
Load the beginner’s three-by-three board
Choose Load beginner board. Start at Edits 0 with no lines or crosses. Read cell clues from top left, one row at a time:
2 2 1 2 2 1 1 1 0
H labels a horizontal edge: its first number is its dot row, from 1 to 4, and its second number is its position across that row, from 1 to 3. V labels a vertical edge: its first number is its row interval, from 1 to 3, and its second is its dot column, from 1 to 4. For example H1-1 joins the top-left dot to the dot directly to its right. V1-3 joins the third dot of the top row to the third dot of the next row.
Try H4-3, the bottom side of the 0 cell. First it becomes a line: Edits 1, and the 0 no longer matches. Select it again: it becomes a cross, the line disappears, and Edits becomes 2. Select it a third time: it becomes unmarked, Edits 3. Undo returns the cross at Edits 2. Now Retry this board so the actual solving route begins at zero.
Build an eight-line loop you can check
The 0 cell tells you that H3-3, H4-3, V3-3 and V3-4 must carry no lines. Keep those empty. For this first complete example we will draw a loop around the upper-left block of four cells, then check that it fits every clue. The route is a worked construction, not a deduction claiming that every intermediate side is forced by one local rule.
- Draw H1-1 along the top, from dot column 1 to 2. Edits 1.
- Continue across H1-2 to dot column 3. Edits 2.
- Turn down through V1-3. Edits 3.
- Continue down through V2-3 to dot row 3. Edits 4.
- Turn left along H3-2. Edits 5.
- Continue left along H3-1 to the first column. Edits 6.
- Turn upward through V2-1. Edits 7.
- Close the route through V1-1, back to the start. Edits 8.
On the last change the eight segments form one closed group, and each used dot has exactly two segments. There are no loose ends, branches or crossings. The edge buttons lock after the win and focus moves to Undo, so you can reopen the previous state or retry the board.
Check all nine cell totals
row 1: 2 2 1 row 2: 2 2 1 row 3: 1 1 0
Each of the four cells inside the loop has two bordering outer sides. The right-hand cells in rows 1 and 2 each touch one vertical side. The bottom cells in columns 1 and 2 each touch one horizontal side. The bottom-right 0 touches none. Thus every clue matches, even though five of the nine cells are outside the loop. The total of cell clues is not the line count, because a shared side can contribute to two clues and a boundary side to only one.
Test what an incomplete loop means
After the win, Undo once. Which edge disappears, how many open ends remain, and does the drawing still satisfy every clue?
Reveal the seven-line check
V1-1 disappears, returning to Edits 7 and seven line segments. Its two endpoint dots each have degree one, so there are two open ends. The top-left cell loses one bordering side: it has 1 of its required 2. The drawing has one connected group but is not closed and does not match all clues. A connected line is not automatically a completed loop. Replacing V1-1 finishes again.
Choose a new attempt deliberately
Retry this board clears every mark and the undo history while retaining the current clues. Load beginner board restores this exact example after another puzzle. New puzzle switches to a different checked clue set in a finite seven-puzzle collection and starts over; the collection eventually repeats. It is not an unlimited generator or a claimed difficulty scale.
A fixed practice address reloads the same example after refresh, but the lines, crosses and history are lost. Ordinary visits restart the collection. There is no account, timer, payment, saved leaderboard or advertising action required. This tutorial teaches a way to read and check one puzzle; it makes no promise about health or general reasoning ability.