Number Trail
Fill every empty square with a number so that 1, 2, 3 and on up to the last number form one trail through the whole grid. Each number touches the next one by a side or a corner. Every puzzle has one solution you can reach by logic alone.
How to play Number Trail
How to play
Drag from a number into an empty square beside it: the next number goes there, and the trail keeps growing as you drag on. Drag back to take numbers off again. If the next number is already on the board, the drag counts down instead. You can also tap a square and pick a number: the buttons above the pad offer one more or one less than the numbers around it, or type any number on the pad or keyboard (arrow keys move, Enter places, Backspace erases). Undo takes back a whole drag.
The rules
The grid holds every number from 1 up to its number of squares (36 on a 6×6) exactly once, and each number touches the one after it, by a side or a corner. Given numbers are bold with a small brass pin; 1 and the last number are always given and framed. A blue line joins each pair of consecutive numbers that touch. A dashed ring marks a number that appears twice or does not touch the next one, and the message under the board says what is wrong.
Techniques
Start where only one number is missing: if 7 and 9 are placed, 8 must touch both, and often just one square does. A number that already touches one of its trail neighbours and has only one empty square beside it sends the other neighbour there. Then count distances: if 8 is missing and the nearest placed numbers are 5 and 12, it is at most 3 steps from 5 and at most 4 from 12, diagonal steps included. On the 10×10 grid, count the steps around numbers that are in the way.
Levels and daily
The 6×6 puzzles need only the neighbour steps. Every 8×8 needs counting distances at least once, and every 10×10 needs counting around the numbers in the way. The daily puzzle is an 8×8, the same for everyone, and changes at midnight UTC.
Questions
What are the rules of Number Trail?
Fill the grid with the numbers from 1 up to the number of squares, each once, so that every number touches the next one by a side or a corner. Together they form one trail that starts at 1, ends at the last number and passes through every square.
Do diagonal moves count?
Yes. A number may touch the next one by a corner as well as by a side, so a square can have up to eight neighbours, and the trail may cross itself diagonally.
Does every puzzle have exactly one solution?
Yes. Every puzzle was checked by a search that tries every possible trail and found exactly one, and solved by a step-by-step solver that uses only logical deductions, so you never need to guess.
Any tips for solving it?
Fill the gaps where only one number is missing first, then look at numbers with only one empty square beside them. When those run out, count how far each missing number can be from the numbers before and after it. Hint finds the next step from your position, fills it in and explains why; if one of your numbers is wrong, it takes that away first.
Is there a daily Number Trail puzzle?
Yes. The daily puzzle is an 8×8 that is the same for everyone and changes at midnight UTC. Earlier dailies are under Past dailies.