Lead the mouse to the cheese through a grid of doors, stepping only to a next-door door that is different in exactly the right number of ways. Or pick the one route that follows the rule. Six levels, a daily set and printable worksheets.
A grid of doors sits on the screen. A mouse waits at the top-left door and a piece of cheese is behind the bottom-right door. The mouse may only step up, down, left or right to a door next to it, and the step must follow a rule about what changes between the two doors. Each door has two or three things to compare: its shape (square, arch or house), its pattern (plain, striped or dotted) and, from level 2, its window (none, round or square). The game says it as step to a next-door door that is different in exactly one way: the next door must differ in one of those things and match in the others. The doors are drawn once at full size with nothing on top of them, and a tap on a door adds it to the walk. Checking a rule step by step against several attributes is the skill that this game trains, and it is the kind of task used in children's computing and logic contests. A child does not need to read much: the rule is written in a few words and the doors carry the evidence.
Level 1 is a 3 by 3 grid with two things on each door, shape and pattern. The rule is a next door that is different in exactly one way, and the shortest route is 4 or 6 steps. Level 2 adds the window as a third thing, still with exactly one change, and the shortest route is 6 or 8 steps. Level 3 keeps three things and changes the rule to different in exactly two ways at every step. Level 4 is a choice: the doors are shown once, and four small maps show four routes from the mouse to the cheese, each walking door to door, and exactly one of them follows the rule at every step. The rule is one or two changes. Level 5 is a 4 by 4 grid with a rule of one or two changes and a shortest route of 8 or 10 steps. Level 6 is the 4 by 4 choice again, and the rule can be different in one way, two ways or all three ways. In the tap levels any path that follows the rule counts, up to 12 steps, not only the shortest.
A puzzle starts with a walk from the top-left door to the bottom-right door of the right length. The doors along the walk are built to follow the rule, and every other door is chosen at random. The game then searches the grid and keeps the puzzle only if the shortest rule-following route has the length that level promises. In a choice puzzle it lists every simple path from the mouse to the cheese of a similar length, picks one that follows the rule and three that break it, and shows the four as small route maps in a random order, beside the doors rather than over them. Where it can, some wrong paths break the rule at only one step, so they look right at a glance. The tests repeat these checks on 500 seeds for every level with their own search: a rule-following route always exists, the shortest route is the length promised, and in a choice puzzle exactly one of the four paths follows the rule and the others are real walks between doors.
Print a worksheet by choosing the level, 4, 6 or 8 puzzles, and Letter or A4 paper. Each sheet has new grids and the last page is an answer key. A worksheet is printed in black and white, so what changes between doors is only ever a shape, a pattern or a window, and all the doors in one puzzle share one colour on screen. The daily set, Today's 5, is made from the date on your device, so a child who plays on two devices on the same day sees the same five puzzles. The game has no timer by default, no ads inside the play area and no account, and a speaker button reads each prompt aloud with your device's voice. It does not hide the rule, it does not count diagonal steps and it does not teach programming. Progress is saved in this browser only.
Compare the door the mouse is on with the door it steps to. If the two doors have different patterns but the same shape and the same window, the doors are different in exactly one way. If the pattern and the shape both differ, they are different in two ways, which is too many for this rule.
Yes. The game builds each grid around a route that follows the rule and then checks the grid with a search. The tests repeat that check on 500 puzzles for every level. In the tap levels any route that follows the rule counts, up to 12 steps.
It shows four route maps from the mouse to the cheese. One follows the rule at every step and the other three each break it at one or more steps. The tests check every puzzle in 500 seeds for levels 4 and 6: exactly one of the four paths follows the rule.
No. A step goes up, down, left or right to the door next to the mouse. A diagonal door counts as not next door.
Choose a level, 4, 6 or 8 puzzles and Letter or A4. The sheet is made in your browser from new grids each time, in black and white, and the last page is an answer key. Nothing is uploaded.
Only in this browser, on this device: the level, stars and daily progress are saved in local storage and nothing is sent anywhere. The page counts visits with Google Analytics, never answers. Clearing site data for this page removes the saved progress.