Codebreaker* vs Shikaku

Following the hints, solve the secret code consisting of four different colors. A black dot means that one of the colors is guessed and located in the correct position. A white dot means that one of the colors is guessed but located in the wrong position.

Shikaku is a logic puzzle with one rule. Divide the grid into rectangles. Every rectangle holds exactly one number, and that number is how many squares it covers. Cover the whole grid and the puzzle is solved. That is the entire rulebook. There is no tutorial to sit through — the first boards are small enough that the answer is nearly visible, and by level ten you are genuinely working. ONE ANSWER, ALWAYS Every board is checked for a unique solution before you ever see it. There is never a moment where you have to guess and hope. Anything you can work out, you can prove. IT CATCHES THE MOVE THAT BROKE IT A rectangle can obey every rule and still make the rest of the puzzle impossible — leaving a number with nowhere to go, or a square nothing can reach. Shikaku tells you at the move that caused it, instead of letting you discover it twenty moves later with no idea where it went wrong. MISTAKES COST SOMETHING. FUMBLES DO NOT. Dragging across a rectangle you already placed is a mis-swipe, not an error, and costs nothing. Change your mind mid-drag, come back to where you started and let go — that cancels, free. Only real reasoning errors count against you. Three per puzzle. SEVEN DIFFICULTIES Gentle, Easy, Medium, Hard, Expert, Master and Grandmaster. The hard tiers are not simply bigger boards — a Grandmaster puzzle has fewer, larger rectangles and far less that can be read off at a glance. It is close to pure deduction. WRITE DOWN WHAT YOU KNOW Switch to marking and drag across the line between two squares to note that they belong in the same rectangle. A mark is a note to yourself and nothing more: the game never checks one against the answer, and marking costs nothing. On a hard board it is how you keep hold of what you have already proved. A NEW PUZZLE EVERY DAY The Daily Challenge is free forever. Keep it up for seven days running and you earn hints. A calendar shows every day you have played, and a day you missed can still be played. It will not mend a streak, but it is there. THREE THEMES Midnight, Slate & Teal, and Forest & Brass. Switch whenever you like. THIS WEEK One weekly board, and it resets every Sunday. It lives on your device, so there is no sign-in, no account and nothing to join — it simply works. The twelve names beside yours are the game's own rivals, marked as rivals on every row, and they do not wait for you. FRAMES YOU EARN Eight frames for your avatar, each one evidence of something you actually did: a seven-day Daily streak, a hundred puzzles solved, a Grandmaster board, a week finished in the top three. They show on the weekly board, and the rivals wear theirs too. YOUR PROGRESS IS YOURS Put it down mid-puzzle and it is exactly where you left it. Your progress lives on your device, and there is no account to make. WHAT IS FREE AND WHAT IS NOT Shikaku is free to play, with every level and every tier, and the Daily Challenge is free forever. Ads are how it pays for itself: a banner on the home, calendar, leaderboard and game screens, an occasional full-screen ad between levels, and optional videos for a hint or a second chance. One payment removes them for good and unlocks every theme. No subscription. No account. No lives, no timers, and nothing to wait for.